TOOLS · US MACHINE SCREW SIZES
#2 machine screw size
This page is about the screw itself: what diameter a US machine screw size number means, which thread counts go with it, and which metric size is closest. Hole and tap drill sizes are on the tap drill chart, the complete unified inch thread table (UNC, UNF, UNEF, UN and UNS, including diameters above 1 in) is on the thread chart, and metric machine screws from M1.6 to M10 are on their own chart.
Answers first
Nominal diameter
0.0860in
(2.184 mm) · source
UNC — coarse
56
UNC pitch: 0.454 mm
UNF — fine
64
UNF pitch: 0.397 mm
Other series
—
Closest metric size
M2
2 mm · +0.184 mm · calculated
Series tabulated
2
Size number 2 ✓ d = 0.0860 in
Nominal (basic) diameter, not a tolerance. Metric comparison is by diameter only and does not make the parts interchangeable.
#2 machine screws: nominal diameter 0.0860 in (2.184 mm), tabulated in 2 thread series in this range, and closest to M2 in metric machine screw sizes.
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Machine screw head types and drives
Machine screws are made with several head shapes and several drive recesses. The names and the uses below are given so that a callout or a drawing can be read; the dimensions of these heads are not reproduced here.
Pan head
The general-purpose head: a low rounded top with a flat bearing face, used where the head sits on the surface.
Flat head (countersunk)
Sits flush in a countersunk hole; the head angle has to match the hole angle, and it centres the joint as it is tightened.
Oval head (raised countersunk)
A countersunk head with a rounded top that stands slightly above the surface, used where a decorative profile is wanted.
Truss head
A wide, low head that spreads the load over a larger area, used on thin sheet and on soft materials.
Binding head
A slightly domed head with a small undercut, traditionally used on electrical and instrument work.
Fillister head
A tall, cylindrical head with a flat top, used where a deeper drive recess is needed.
Hex head
A hexagonal head turned with a wrench rather than a screwdriver, used where more tightening torque is needed.
Socket head cap
A cylindrical head with an internal hex recess, tightened with a hex key and able to take high torque in a small space.
Drive recesses
Slotted — The original drive: a single slot, usable with a plain screwdriver, and still found on older equipment.
Cross recess (Phillips type) — The most common cross recess: the driver centres itself, and the recess cams out before the head is overloaded.
Internal hex socket — Takes a hex key, which allows higher torque and a smaller head than an external drive.
Six-lobe (Torx type) — Six lobes with more driving area than a cross recess, used where the head is small or the torque is high.
Square recess — A square recess that resists cam-out and can be driven one-handed where access is difficult.
Combination slotted and cross recess — A recess that accepts either a slotted or a cross-recess driver, used where the tools at hand are unknown.
Head and drive recess dimensions — head diameter, head height, recess width and depth — are tabulated in ASME B18.6.3. The names above are given so that a callout can be read; dimensions for a specific head should be taken from that standard or from the supplier's drawing.
Drill and tap sizes for machine screws
The hole a machine screw passes through, and the hole that is tapped to receive it, are separate questions from the screw's own dimensions, and they depend on the fit that is wanted.
Tap drill sizes for the unified inch series are on the tap drill chart, per series and per size, with the nearest standard drill. Only some of the sizes in this range have a drill value tabulated there, and the size pages link to those that do.
Drill designations come in four notations — number drills, letter drills, fractional inch drills and millimetre drills — and a hole size can be written in any of them. The three notations that come up with machine screws (number, fractional and metric) are listed side by side on the drill bit size chart, so the drill that a drawing calls for can be found in the set on hand.
Thread series tabulated for #2
The same nominal diameter with the thread counts that go with it. A coarse and a fine thread on one diameter are not alternatives for the same part: the hole and the tap differ as well.
| Series | Callout | Threads per inch | Pitch (in)ᶜ | Pitch (mm)ᶜ | Basic pitch diameter d2 | Basic minor diameter d1 | Basis |
|---|---|---|---|---|---|---|---|
| UNC | #2-56 UNC | 56 | 0.0179 | 0.454 | 0.0744 | 0.0667 | read from FED-STD-H28/2B appendix A |
| UNF | #2-64 UNF | 64 | 0.0156 | 0.397 | 0.0759 | 0.0691 | read from FED-STD-H28/2B appendix A |
Read from the source: nominal major diameter and threads per inch, row by row. Calculated here: millimetre values (inch × 25.4), pitch (P = 1 / threads per inch), basic pitch diameter and basic minor diameter from the 60° basic thread form, and the nearest metric size by nominal diameter.
Diameters are quoted as nominal (basic) sizes for engineering and purchasing reference. They are not limits of size and not interchangeability values.
#2 in full
One row per thread series tabulated for this size, with the basis of each value stated so the source values can be told from the calculated ones.
| Parameter | Value | Basis |
|---|---|---|
| Nominal major diameter d | 0.0860 in / 2.184 mm | read from FED-STD-H28/2B appendix A |
| Closest metric size | M2 (2 mm, +0.184 mm) | calculated on this page |
| Size number 2 → d | 0.0860 in | matches the table |
Other series on this diameter
Beyond the coarse and fine series, the source tables other series on some diameters of this range. They are read the same way.
No further series is tabulated on this diameter in this range.
Going further with this screw
No tap drill value is tabulated for this size
The tap drill chart does not carry a row for this size; the nearest sizes that do are linked from the size chart.
- Drill bit size chart →
Number, fractional and metric drill designations side by side, so the drill a drawing calls for can be found in the set on hand.
- Metric machine screws near this size →
The metric track: the size chart for metric machine screws M1.6 to M10, with head dimensions, drive sizes and the nearest US size.
- Unified inch thread chart →
The complete thread data for this series: threads per inch, pitch, basic pitch diameter and minor diameter, size by size.
Where these numbers come from
The diameters and thread counts on this page are the size and thread data of FED-STD-H28/2B, appendix A, tables II.A.1 and II.A.2 — a US federal standard. Each row of the table can be traced back to its line in the source data file by the line number given on the size pages. Millimetre values are a straight conversion of the inch value; pitch and thread-form values are calculated, not quoted from the table.
What is covered
The size numbers from #0 to #12 are tabulated in full: 10 size numbers and 20 diameter and thread count rows, of which 19 were accepted directly from the source and 1 was recovered after review. The fractional sizes 1/4 in to 1/2 in are also tabulated, 5 sizes and 28 rows.
Rows accepted after review
- #4-48 UNF
1 row in this range could not be read cleanly from the source scan and was recovered from a second, independent source together with the size and thread count arithmetic. It is named below rather than silently included.
What is not covered
Size #14 is not tabulated here. The source used for this chart ends its numbered sizes at #12, so #14 is left out rather than filled in from a supplier chart. The source does contain a further 221 fractional rows from 1/4 in up to the largest size, but only the machine screw part of that range — 1/4 in to 1/2 in — is repeated on this page; sizes from 9/16 in and larger are on the unified inch thread chart. Head and drive recess dimensions are not given here; take them from the current standard or the supplier's drawing.
Coverage: This page is one of the 15 sizes in the machine screw range that have a page of their own; the full table of this range is on the size chart.
Sources for this size
- FED-STD-H28/2B — Unified Inch Screw Threads UN and UNR (US federal standard; appendix A size and thread data)
- Yaxiio metric size tables — machine screw sizes used for the metric comparison column
- ASME B18.6.3 — the current standard for machine screw and machine screw nut dimensions, cited for the current designation
Values on this page are taken from the sources listed and computed here as described; the sources' typography and additional columns are not reproduced.
Send the callouts, get the matching machine screws quoted
If your drawing, picking list or enquiry sheet uses US machine screw callouts — or mixes them with metric ones — send the list across and we will read it to size, thread count, head type and drive, and quote the parts against it. We work as a trading partner and solution provider: the enquiry is read as a specification, and what comes back is a quotation with the parts, the surface finish and the documents that go with them.
- Callouts as written, including size number or fractional diameter, thread count and head type
- Quantities per size, and whether a fine thread is needed or the coarse one will do
- Material, surface finish and any part marking or documentation the job requires
- Where the parts go, so the specification can be checked against the working conditions
Checking a tightening value instead?
The torque calculator turns a preload target or a friction state into a tightening torque, and the torque charts give the values tabulated by diameter and grade.
Cite this chart
YAXIIO. #2 machine screw size. https://www.yaxiio.com/en/tools/machine-screw-size-chart/no-2 (accessed 2026-10-29).
Free to cite and embed — attribution required: “YAXIIO” + a link to this page.
Frequently asked questions
What diameter is #2?
#2 machine screws have a nominal major diameter of 0.0860 in, which is 2.184 mm. The value is nominal (basic): the limits of size for a finished screw are tighter and are set by the thread class.
What thread counts are tabulated for #2?
UNC 56 threads per inch; UNF 64 threads per inch. Pitch follows from the thread count: P = 1 / threads per inch. All series tabulated on this diameter, with their pitch and diameter values, are in the table above.
What is the closest metric size to #2?
M2, whose nominal diameter is 2 mm, against 2.184 mm here, a difference of +0.184 mm in nominal diameter. The thread counts are not the same, so this is a read-across for drawings, not a substitution: a metric screw of the nearest diameter will bind in a tapped hole cut for this size.
Which drill and which tightening torque go with #2?
Both are outside this page: the screw's own dimensions are given here, the hole and tap drill size are on the tap drill chart, and tightening values are on the torque charts. The nearest sizes that have a drill value tabulated are linked from the size chart.
Related References
Unified inch thread chart
The full thread data for UNC, UNF, UNEF, UN and UNS: threads per inch, pitch, basic pitch diameter and minor diameter, including diameters above 1 in.
Tap drill chart — UNC and UNF
The hole to drill before tapping, by series and size, with the nearest standard drill from the inch drill set.
Screw size chart — metric machine screws
The metric track: head dimensions and drive sizes for metric machine screws M1.6 to M10, with the nearest US machine screw size.
Drill bit size chart
Number, letter, fractional and metric drill designations side by side, so the drill a drawing calls for can be found in the set on hand.
Sizes on this page are nominal (basic) values compiled for design and purchasing reference. They are not tolerances and not inspection limits. Fastener dimensions must be verified against the governing standard and the drawing before production.