TOOLS · SOLAR CLAMP SIZES
Solar Panel Clamp Size Chart: 30–45 mm Module Frame Thickness
This page answers one question: which clamp a module frame thickness calls for, and what pairs with it. The frame thickness bands run from 30 to 45 mm, the end clamp and the mid clamp take the same band, and the bolt in the whole series is M8. It is not a mounting-system design: the clamp grip height, the rail section, the clamp spacing and the tightening value are set per project, and they are given here as rules, not as tabulated numbers. For the surrounding fastener data, the bolt size chart covers hex bolts, the torque charts cover tightening values, and the nut and washer charts cover those parts.
Clamp size by module frame thickness
| Module frame thickness (mm) | End clamp grip size (mm) | Mid clamp grip size (mm) | Paired bolt | Hex nut s × m (mm) | Flat washer D × t (mm) | Minimum bolt length floor (mm) |
|---|---|---|---|---|---|---|
| 30 | 30 | 30 | M8 × 1.25 | 13 × 6.5 | 16 × 1.6 | 38.1 |
| 32 | 32 | 32 | M8 × 1.25 | 13 × 6.5 | 16 × 1.6 | 40.1 |
| 33 | 33 | 33 | M8 × 1.25 | 13 × 6.5 | 16 × 1.6 | 41.1 |
| 35 | 35 | 35 | M8 × 1.25 | 13 × 6.5 | 16 × 1.6 | 43.1 |
| 38 | 38 | 38 | M8 × 1.25 | 13 × 6.5 | 16 × 1.6 | 46.1 |
| 40 | 40 | 40 | M8 × 1.25 | 13 × 6.5 | 16 × 1.6 | 48.1 |
| 42 | 42 | 42 | M8 × 1.25 | 13 × 6.5 | 16 × 1.6 | 50.1 |
| 45 | 45 | 45 | M8 × 1.25 | 13 × 6.5 | 16 × 1.6 | 53.1 |
One row per frame thickness band. The band is the frame thickness the clamp is made to grip; the end clamp and the mid clamp take the same band. The bolt, the washer and the nut are read from the in-repo fastener source and do not change across the series.
The bands are the thicknesses this series is supplied for. They are not a standard series: the clamp is a non-standard part made to drawing, so the grip height, the jaw depth and the body dimensions are confirmed per order on the drawing. The last column is a floor, not an order length: it counts the frame thickness, the washer and the nut only, and the clamp body and the rail wall still have to be added.
Intermediate steps in the series: 32, 33, 38 and 42 mm. Each of them is a band of its own above, with its own row and its own page, so a measured frame thickness does not have to be rounded onto a coarser step.
The floor in the last column is derived on this page from the band and the two in-repo dimensions next to it, so it can be recomputed row by row. Everything else in the table is read from the sources named at the foot of the page.
Read from the sources: the bolt diameter and pitch, the hex nut across flats and height, the flat washer outside diameter and thickness, and the flange nut across flats, height and flange diameter. Calculated here: the end clamp and the mid clamp take the band itself, and the minimum bolt length floor is the frame thickness plus the flat washer thickness plus the full height of the hex nut.
Full PDF
Download the full PDF (30–45 mm, all sizes)
Printable chart covering every size in this family — enter your email to get it.
Frame thicknesses with their own page
Every band in this series opens a page with its own row, the neighbouring bands side by side, the material boundary for that band, and the cross-band check.
How to measure the frame thickness and pick the clamp
The measurement decides, not the label. A module frame is measured on the flange the clamp grips, with the module off the roof and the flange clean, and the reading decides the band.
Measure the flange the clamp grips
Use a caliper on the aluminium flange, not a tape on the frame's overall depth: the dimension that matters is the thickness of the flange the jaw closes on. Take three readings along the flange, because an extruded profile is not perfectly uniform, and keep the largest. If the module is already on the roof, measure at the end of a row where the flange is accessible.
caliper, flange clean, three readings
Read the band off the table
Take the largest reading and find it in the table above. Both the end clamp and the mid clamp take that same band, so there is one number to order per project, not two. If the reading lands between two bands, order the band the supplier's stated range covers; where the supplier sells the clamp as a range rather than as a single thickness, the range is the item that has to contain your reading.
the band table above
Check the array edge separately
At the end of a row one jaw of the end clamp closes on a single module flange, while a mid clamp shares the load between two. The band stays the same, but the edge is the position that fails first under uplift, so the edge fittings and the fixing count there are taken from the structural calculation — do not carry the mid-clamp assumption to the row end.
uplift load at the edge
The three steps are a selection method, not a standard procedure. Grip height, jaw depth and the permitted tolerance on the flange are drawing values for the specific clamp and are not tabulated on this page.
Will a 35 mm clamp fit a 30 mm frame?
Sometimes, and the deciding item is the grip range the supplier states for that clamp — not the number in its name. A clamp sold as a single thickness grips that thickness; a clamp sold as a range covers the bands inside the range. Go by the range, and check the two failure directions below before you use what is on the shelf.
| Your clamp against your frame | Verdict | What it turns on |
|---|---|---|
| The frame thickness falls inside the grip range stated for the clamp | Fits, as stated | the grip range printed on the supplier's drawing or data sheet for that specific body |
| The frame is thinner than the range the clamp is stated for | Do not fit it | your own caliper reading on the actual flange, not the module data sheet |
| The frame is thicker than the range the clamp is stated for | Do not fit it | your own caliper reading on the actual flange, not the module data sheet |
Fails by not gripping
A clamp stated for a thicker frame has its jaw opening deeper than the flange is thick. The body bottoms out on the rail shoulder before the jaw closes on the frame, so the module is held by friction alone or not at all; the joint looks tight on the day and works loose under repeated uplift. Nothing in the assembly shows it, so it survives the handover and fails in the first storm season.
Fails by riding on the flange
A clamp stated for a thinner frame cannot open far enough. It closes on the top corner of the flange or on the frame edge instead of on the flange face, and the load path is no longer flat on flat: the flange deforms, and the load arrives at the glass edge. This is the direction that damages the module, and the damage often appears after the clamp is already tight.
Go up or down to the band your reading falls in, or use a clamp whose stated range contains it. A pad or a shim changes what the bolt stack measures, not what the jaw spans, so it does not rescue a wrong band.
Both directions are engineering consequences of the jaw opening against the flange thickness, not a quotation of any supplier's table. Where the supplier states a range, that range is the governing item, and it is a drawing value.
End clamp and mid clamp: same band, different job
This is the part of the question that catches people out: the end clamp and the mid clamp are ordered in the same band as the frame thickness. What differs is the body and the load path, not the number.
| Clamp | Where it sits | What it holds | How the load arrives | What changes at the array edge |
|---|---|---|---|---|
| End clamp | The outer flange of a single module, at the end of a row or the edge of the array. | One module flange, with the jaw closing on one side only. | Uplift enters the clamp through a single flange, so the same wind pressure loads one jaw instead of two and the moment about the clamp is not balanced by a neighbouring module. | The end position is the one that fails first, so the edge zone, the rail end and the fixing count there come from the structural calculation even though the band does not change. Edge strengthening is a separate fitting, not a bigger clamp band. |
| Mid clamp | Between two module flanges, sharing one clamp body across the pair. | Two module flanges, one under each side of the same jaw. | Uplift from two modules arrives at the same body, and the two sides largely balance each other under uniform pressure. | Nothing changes at the edge for a mid clamp: by definition it is not the end position. Do not substitute one for an end clamp to save a line item. |
Both bodies in this series take the same frame thickness band and the same M8 bolt. The difference is geometry and load path; it is not a size step.
Material boundary for coastal, industrial and floating jobs
The clamp body is supplied anodized aluminium. Where the working conditions attack aluminium faster than the site can maintain it, the body moves to stainless steel and the fasteners and the isolation go with it. This page gives the boundary by working condition; it does not give material grades, because those are drawing values.
The two body directions
| Body as supplied | Where it is the default | What it means for the set |
|---|---|---|
| Anodized aluminium body | Inland and ordinary urban sites | The anodized layer is the corrosion protection and it is also an electrical insulator, so it must not be broken at the contact face where the washer and the bolt sit. |
| Stainless steel body | Shore sites, plant surrounds, floating and splash zone installations | It costs more per piece, and it changes what has to be isolated against the aluminium rail or frame: the bolt, the nut and the washer move with it rather than being chosen separately. |
- Coastal: salt-bearing air, shore sites and anything within sight of surf
- Industrial: chemical or acidic air, plant surrounds and waste or fertiliser installations
- Floating and splash zone: water surface, spray and permanent moisture
Band by band
The boundary does not change with the band: every thickness in the series is supplied the same way. What this table fixes is that the odd steps carry the same material answer as the round ones, so a project with a 33, 38 or 42 mm frame is not left guessing.
| Frame thickness band (mm) | Body as supplied | Upgrade to stainless when | What is checked with it |
|---|---|---|---|
| 30 | Anodized aluminium body | coastal — salt-bearing air · industrial — chemical or acidic air · floating or splash zone | the bolt, the nut and the washer move to stainless at the same time, and the aluminium-to-stainless contact is isolated so the pair cannot form a galvanic cell in rainwater |
| 32 | Anodized aluminium body | coastal — salt-bearing air · industrial — chemical or acidic air · floating or splash zone | the bolt, the nut and the washer move to stainless at the same time, and the aluminium-to-stainless contact is isolated so the pair cannot form a galvanic cell in rainwater |
| 33 | Anodized aluminium body | coastal — salt-bearing air · industrial — chemical or acidic air · floating or splash zone | the bolt, the nut and the washer move to stainless at the same time, and the aluminium-to-stainless contact is isolated so the pair cannot form a galvanic cell in rainwater |
| 35 | Anodized aluminium body | coastal — salt-bearing air · industrial — chemical or acidic air · floating or splash zone | the bolt, the nut and the washer move to stainless at the same time, and the aluminium-to-stainless contact is isolated so the pair cannot form a galvanic cell in rainwater |
| 38 | Anodized aluminium body | coastal — salt-bearing air · industrial — chemical or acidic air · floating or splash zone | the bolt, the nut and the washer move to stainless at the same time, and the aluminium-to-stainless contact is isolated so the pair cannot form a galvanic cell in rainwater |
| 40 | Anodized aluminium body | coastal — salt-bearing air · industrial — chemical or acidic air · floating or splash zone | the bolt, the nut and the washer move to stainless at the same time, and the aluminium-to-stainless contact is isolated so the pair cannot form a galvanic cell in rainwater |
| 42 | Anodized aluminium body | coastal — salt-bearing air · industrial — chemical or acidic air · floating or splash zone | the bolt, the nut and the washer move to stainless at the same time, and the aluminium-to-stainless contact is isolated so the pair cannot form a galvanic cell in rainwater |
| 45 | Anodized aluminium body | coastal — salt-bearing air · industrial — chemical or acidic air · floating or splash zone | the bolt, the nut and the washer move to stainless at the same time, and the aluminium-to-stainless contact is isolated so the pair cannot form a galvanic cell in rainwater |
Aluminium in contact with stainless steel forms a galvanic couple as soon as rainwater bridges the two, and the aluminium is the side that goes. Clamp bodies, rails and frames are usually aluminium while the bolt, the nut and the washer are stainless, so the isolation between the two metals is a designed item, not an accessory: it is the reason a washer is specified rather than optional. If the isolation is omitted, the corrosion shows up as white oxide at the contact face long before the module is due for replacement.
The boundary above is an engineering judgement by working condition, not a standard classification. The classification tables that use numbered corrosion categories are published in a locked standards document and are not quoted here, and body grades are drawing values: ask for the grade you need in the enquiry rather than reading one off this page.
Clamp spacing by load zone: the method, not a table
Spacing is the one column this page deliberately does not tabulate. It is not a property of the clamp: it falls out of the load the site puts on the array and the capacity of the fixing, so the same clamp has a different spacing on a low inland roof and on an exposed coastal edge.
Uplift or snow load per unit area × the area one fixing carries ≤ the capacity of that clamp, bolt and rail connection
What has to be in hand before a spacing can be fixed
- the wind and snow zone for the site, and the uplift coefficient that goes with the roof or terrain
- the module area each fixing carries, which sets the tributary area on the clamp
- the rail section and the pull-out or slip capacity of the clamp, bolt and rail connection
- the edge and corner zones, where the same clamp carries more uplift on the same tributary area
The two ways a spacing comes out wrong
Slip under uplift
Spacing too wide means the clamp is asked for more load than its connection holds. The failure is progressive: the joint slips a fraction, the preload drops, and the next gust slips it further. It is seen as a row that has drifted or a rail with bright witness marks at the bolt.
Flange or glass damage
Spacing too tight means the clamp is asked for load it can carry but the module flange is not, and the force arrives at the aluminium frame next to the glass edge. The module cracks at a clamp position, usually at a corner of the array where the load is highest. Tightening harder makes this direction worse rather than better.
If you already have a spacing figure from another source, treat it as that source's assumption and not as a property of this clamp: a spacing copied from a table without its load case is the one number that cannot be checked.
The bolt and the accessories in this series
The whole series pairs with one bolt size, so the accessories are a single set rather than a column that changes from band to band. All values below are read from the in-repo fastener source.
Bolt nominal diameter d
8
from the in-repo source
Bolt coarse pitch P
1.25
from the in-repo source
Hex nut across flats s
13
from the in-repo source
Hex nut height m
6.5
from the in-repo source
Flange nut across flats s
13
from the in-repo source
Flange nut height k
8
from the in-repo source
Flange nut flange diameter dc
17.9
from the in-repo source
Flat washer outside diameter D
16
from the in-repo source
Flat washer thickness t
1.6
from the in-repo source
Spring washer outside diameter D
14.8
from the in-repo source
Spring washer thickness t
2
from the in-repo source
A flange nut is taller than the hex nut in the same thread by this much, so add it to the floor in the main table when the assembly uses one.
The same bolt, nut and washer apply to every band in the series, including the intermediate steps. Nothing in the accessory set changes when the frame thickness changes: only the length of the bolt follows the frame, through the floor in the main table.
The nut values are the supply dimensions of that part, read from the in-repo source. Where a project calls for a standardised nut, quote the standard you need in the enquiry and the counterpart is confirmed on the drawing.
Two washer forms are tabulated because both are read from the same in-repo source: the flat washer and the spring washer. Serrated or ribbed lock washers are the third form used in this duty, and their dimensions are not in the in-repo source, so they are listed under what this page does not tabulate rather than guessed at. The washer bore does not change the bolt it pairs with.
Tightening the M8: method and preconditions, no value here
This page does not print a tightening torque. A torque value belongs to a bolt with a known property class, and the class on a clamp bolt is a drawing value: the same M8 can be supplied in different classes and the correct torque moves with it. The method is the K-factor relation, and the input the K range stands for is listed in the torque chart family.
T = K × F × d
Before a torque can be stated, the property class of the bolt has to come from the drawing or the batch inspection report, and the preload the joint is designed for has to come from the structural calculation. Neither is fixed by the frame thickness, so neither can be tabulated per band.
The greased or dry condition of the thread, the presence of the washer and the coating on the bolt all move the torque for the same preload, which is why the K range in the torque charts is given as a band rather than a single number.
K range and torque values per size in the torque charts →What this page deliberately does not tabulate
A value with no source behind it looks like a guarantee. These eight are the ones a reader expects and this page does not print, with the reason for each.
Clamp grip height and jaw depth
The clamp is a non-standard part made to a supplier drawing. There is no standard series behind this dimension, so the value is confirmed on the drawing for the specific body rather than quoted here.
Clamp body length, width and thickness
The clamp is a non-standard part made to a supplier drawing. There is no standard series behind this dimension, so the value is confirmed on the drawing for the specific body rather than quoted here.
Rail wall and flange thickness
This is fixed by the mounting system and the module, not by the clamp: it comes from the project drawing, and any figure printed here would be another project's answer.
Clamp spacing values
This one follows from the load case, not from the part. It is calculated for the project, and the method and the inputs are set out above instead of a table.
Serrated lock washer dimensions
The clamp is a non-standard part made to a supplier drawing. There is no standard series behind this dimension, so the value is confirmed on the drawing for the specific body rather than quoted here.
Body material grade and property class
The material grade and property class on the clamp bolt are specified per order. Printing one would narrow the choice of every reader to one project's decision.
Tightening torque value
A torque value depends on the mechanical properties of the bolt class and varies with the class ordered, so the relation and its preconditions are given instead of a generic number.
Numbered corrosion categories
The numbered classification is defined in a standards document; this page works in plain working-condition terms and marks the boundary as an engineering judgement.
Where the data comes from and where to go next
The bolt, the nut and the washer under their own product pages
- Socket head cap screws →
The M8 clamp bolt is usually an internal hex screw. Sizes, lengths and the standard they are supplied under.
- Flange nuts →
The flange nut in this series: across flats, height and flange diameter, supplied to the standard named on the page.
- Flat washers →
The flat washer that sits between the nut and the rail, and the dimensions it is supplied in.
The neighbouring tool pages
- Bolt size chart →
Hex bolt dimensions by size: across flats, head height and thread, for the bolt rather than the clamp.
- Bolt torque chart →
Torque values and K factor ranges by size and property class — the input the tightening method above needs.
- Hex nut weight chart →
Hex nuts by size: across flats and height, with the weight per piece.
- Flat washer weight chart →
Flat washers by size: outside diameter and thickness, with the weight per piece.
- Solar hanger bolt chart →
The other half of a rooftop fixing set: hanger bolt sizes and supply lengths for the roof build-up down to the purlin.
Provenance, coverage and what is out of scope
Every number on this page is either read from an in-repo fastener source or derived on the page from one, and both are named below. Nothing is taken from a supplier catalogue, and no vendor table is reproduced.
Covered here
Frame thickness bands from 30 to 45 mm in 8 steps, each with its own row and page; the end clamp and the mid clamp band for each; the M8 bolt, hex nut, flange nut, flat washer and spring washer that pair with the band; the minimum bolt length floor; the cross-band boundary; the material boundary by working condition; and the selection method.
Not covered here
Thicknesses outside 30–45 mm, including the round values just outside the series such as 28 and 48 mm: a project frame thickness outside the series is quoted from the drawing rather than mapped onto a neighbouring band. Also out of scope: clamp grip height and jaw depth, body dimensions, rail sections, spacing values, material grades and tightening torques — each is listed above with the reason.
Value caliber: The bands are a supply programme, not a standard series: the clamp is a non-standard part made to drawing, so no standard number is quoted anywhere on this page. Bands are given as nominal millimetre values at the flange, without tolerances; the permitted tolerance on a specific clamp body is a drawing value.
Sources
- In-repo metric fastener dimensions: bolt diameter and pitch, hex nut, flat washer and spring washer (M8 row)
- In-repo flange nut supply dimensions: across flats, height and flange diameter (M8 row)
- The frame thickness bands and the clamp grip bands: supply programme, non-standard part, values by supplier drawing
- In-repo knowledge base on PV fastener corrosion and the aluminium-to-stainless galvanic pair
- Numbered corrosion classification: this page works in plain condition terms and does not cite the numbers
- Supplier clamp data sheets: values are confirmed on the supplier drawing; no generic values are listed here
- Clamp spacing: project structural calculation, method and inputs on this page, no values
Of the entries below, the vendor data sheets and the corrosion classification describe selection background only; no value on this page is taken from them.
Ordering the set
The clamp body and the matching M8 fasteners are supplied as one set, with the drawing confirmed before the order is released. Send the frame thickness you measured, the rail section and the load case; the band, the bolt length and the material direction are then confirmed in writing against your project rather than against a catalogue page.
- the frame thickness band, measured on the flange the clamp grips
- the rail section and the wall or flange thickness the bolt passes through
- the end and mid clamp positions, and how many of each the array needs
- the working condition, so the body material and the isolation are fixed together
- the load case for the edge zone, if the project has an exposed edge or corner
Cite this chart
YAXIIO. Solar Panel Clamp Size Chart: 30–45 mm Module Frame Thickness. https://www.yaxiio.com/en/tools/solar-clamp-size-chart (accessed 2026-10-29).
Free to cite and embed — attribution required: “YAXIIO” + a link to this page.
Questions this page answers
What size clamp do I need for a 35 mm module frame?
The 35 mm band. The end clamp and the mid clamp both take the band that matches the frame thickness, so you order one band per project, and the bolt is M8. Measure the flange the jaw closes on rather than the whole frame depth, and use the largest of three readings, because the tolerance on an extruded profile runs along its length.
Is a 35 mm clamp compatible with a 30 mm module?
Only if the clamp you have is stated for a range that contains 30 mm. A clamp stated for a single thickness grips that thickness; a clamp stated as a range covers the bands inside it. If your frame is thinner than the stated range the jaw does not close on the flange at all, and if it is thicker the clamp closes on the flange corner and loads the glass edge, which is the direction that cracks modules.
Do the end clamp and the mid clamp come in different sizes?
Not in this series. Both take the frame thickness band, and both take the same M8 bolt. What differs is the body and the load path: an end clamp closes a single jaw on one flange at the end of a row, while a mid clamp shares its body between two flanges. The edge position is the one that carries uplift on a single flange, so it is checked separately in the structural calculation.
What bolt and washer go with the clamp?
M8 across the whole series, so the pairing does not change when the frame thickness changes. The dimensions of the bolt, the hex nut, the flange nut, the flat washer and the spring washer are read from the in-repo fastener source and listed above. Serrated lock washers are used in this duty too, but their dimensions are not in that source, so they are not tabulated here.
How long does the clamp bolt have to be?
Add four items: the clamp body thickness where the bolt enters, the module frame thickness, the rail wall or flange thickness, and the washer plus the nut. Only the middle items are fixed by the band, so the table gives a floor that counts the frame, the washer and the nut, and the other two come from the drawing. Using a flange nut instead of a hex nut adds the difference listed with the accessories.
When do I need a stainless steel clamp instead of anodized aluminium?
Where airborne salt, process chemicals or permanent moisture reach the clamp for years: shore sites, plant surrounds and floating or splash-zone installations. Inland and ordinary urban sites are the default case for the anodized aluminium body. Whichever direction the job takes, the bolt, the nut and the washer move together and the aluminium-to-stainless contact is isolated, because the galvanic pair between the two metals is what corrodes the aluminium.
Related References
Bolt size chart
Hex bolt dimensions by size: across flats, head height and thread.
Bolt torque chart
Torque values and K factor ranges by size and property class.
Hex nut weight chart
Hex nuts by size, with across flats, height and weight per piece.
Flat washer weight chart
Flat washers by size, with outside diameter, thickness and weight.
Sizes on this page are engineering reference values for selection and purchasing. Clamp dimensions, rail sections and installation values must be confirmed against the drawing, the batch inspection report and the project structural calculation before production or installation.