US Flat Washer Size Chart (USS & SAE Patterns)

MS15795 flat washer size chart (DASH NO. 801–858)

58 dash numbers, in the printed order of the source table: inside diameters ØA from 0.078 in to 3.125 in and outside diameters ØB from 0.188 in to 5.500 in. Thickness C is printed in three columns — basic, maximum and minimum — and the inside and outside diameters each carry their own upper and lower tolerance.

The dash numbers run 801 to 858 with no gaps: the first page of the source table carries 40 rows and the second page 18. Every row that the source table marks with a footnote is labelled in the last column; rows with no footnote are labelled as unmarked preferred sizes.

Values marked ᶜ are calculated on this page; every other value in this table is read from the source table row by row.

Wide vs narrow: two OD patterns on the same hole

The source table lists washers by inside diameter, and 13 of the 40 inside diameters in it carry more than one outside diameter. Where that happens, the same hole can take a washer that covers more or less of the surface. This grouping is taken straight from the table — same inside diameter, different outside diameter — and not from any outside classification.

Wide vs narrow: the eight sizes that have a page

For each of those eight bolt sizes, the two patterns of the table, how far each inside diameter sits above the nominal bolt diameter, and how much bearing area the wide pattern adds. The 1/2 in row is the example used at the top of this page. Both computed columns are worked out here from the table values.

The offsets and the extra bearing area are calculated on this page: the offset is the inside diameter minus the nominal bolt diameter, and the extra bearing area is the wide washer bearing area minus the narrow one, with both bearing areas from the same formula as the main table.

Which one to use

The two patterns differ in outside diameter, so the choice is about how much surface the washer presses on and how much room there is around the fastener. This is guidance for selection, not a requirement set by the source standard.

Wide (USS) pattern

Choose the wide pattern when the surface has to be spread over more area or when the hole is not a tight fit under the head: soft or oversize material, slotted holes, oversized or damaged holes, castings, sheet metal and timber. On the same bolt size it always adds bearing area — the extra area of each size is in the table above.

Narrow (SAE) pattern

Choose the narrow pattern where the washer has to stay inside the footprint of the part: tight assemblies, a counterbore or spot-faced joint, hard washers, close fastener spacing, and where the clearance around the head or nut is limited. It carries the same bolt and the same thickness on the same bolt size, over a smaller ring.

If the drawing, the bill of materials or the customer standard names a dash number, that dash number decides. Where the choice is genuinely open, confirm the bearing area you need and check that the wide pattern still clears the surrounding parts.

Washer ID to bolt size

The source table lists washers by inside diameter, not by bolt size: a washer is called out by its dash number, and the inside diameter is what has to clear the bolt. The inside diameter of every row is larger than the nominal diameter of the bolt it fits, so the bolt passes through and the washer can still be assembled on a joint that is not perfectly aligned.

Our per-size pages are indexed by bolt size instead, because that is how washers are asked for in practice and how the rest of this site is built. The offset column in the table above shows how far each inside diameter sits above the nominal bolt diameter for the eight sizes that have a page; for any other dash number, compare its inside diameter ØA with the nominal diameter of your bolt.

• Metric bolt size chart (width across flats, head height) →
• Unified inch thread chart (UNC and UNF sizes) →

  Nominal diameters and thread counts for the unified inch series, so a callout can be turned into a nominal diameter to compare with the inside diameter of a washer.

Bearing area: π/4·(OD² − ID²)

The bearing area is the ring of metal that the washer presses on the joint. It is the one column of the main table that is calculated here rather than read from the source.

A = π/4 · (ØB² − ØA²)

ØB is the basic outside diameter and ØA the basic inside diameter, both read from the source table; A is the area of the ring between them. The same formula gives the extra bearing area of the wide pattern in the pair table, as the difference between the two patterns on one bolt size.

Values marked calculated are worked out here and are not printed values of the source table: the bearing area A = π/4·(ØB² − ØA²) uses the basic outside and inside diameters, and the inside-diameter offsets use the nominal bolt diameter. The bearing area says how much surface carries the load; it does not replace the dimensions themselves.

The inside diameter ØA, the outside diameter ØB, thickness C and the two tolerances on this page are source values, read row by row from the source table and traceable to its page and row. The bearing area and the offsets are calculated values, reproduced here from the formulas given on this page. The version status of the source is disclosed at the foot of this page.

US vs metric (ISO 7089 / DIN 125)

Both families are flat washers, and both are commonly described in the same places, so the differences are worth stating plainly.

US (inch) flat washer

Sized in inches and called out by dash number, thickness given as basic with maximum and minimum limits, and two outside-diameter patterns on the same inside diameter. The table on this page is this family.

Metric flat washer (ISO 7089 / DIN 125 A)

Sized in millimetres and called out by bolt size, for example an M10 washer for an M10 bolt, with one inside diameter, one outside diameter and one thickness per size. It has its own chart on this site.

The two are not interchangeable. A metric washer and a US washer that look similar can differ in inside diameter, outside diameter and thickness, and a washer that is the wrong thickness changes how much thread is left for the nut. Match the washer to the fastener system on the drawing.

Sources and row-level provenance

Every row of the main table is a dash number from Table I of the US military flat washer standard MS15795G (Washer, Flat-Metal, Round, General Purpose, revision G). This page takes its dimension columns — inside diameter, outside diameter, thickness and the two tolerances — and records them row by row, together with the page and row of the collection file so that a single value can be traced back to where it was read.

What this table covers

All 58 dash numbers of that table, 801 to 858: inside diameters ØA from 0.078 in to 3.125 in, outside diameters ØB from 0.188 in to 5.500 in, in the printed order of the source. The table is split over two printed pages, 40 rows and 18 rows, and both pages are included.

The source's own footnotes, counted

The source table marks only a few rows with a footnote. Rather than describing the whole table as one type, this chart reports the footnotes as they are printed, row by row:

• 50 rows carry no footnote; the source describes the remainder of the table as preferred sizes Type A
• 5 rows are marked as selected Type A
• 1 row is marked Type B
• 1 row is marked nonstandard
• 1 row is marked as superseded by AN960-C4

The rows that carry a footnote

Listed one by one, with the inside diameter of each row, so the type labels are never extended to rows the source does not label:

• MS15795-803 — ØA 0.125 in — Selected Type A (source footnote on this row)
• MS15795-804 — ØA 0.125 in — Superseded by AN960-C4 (source footnote on this row)
• MS15795-805 — ØA 0.156 in — Selected Type A (source footnote on this row)
• MS15795-807 — ØA 0.188 in — Selected Type A (source footnote on this row)
• MS15795-850 — ØA 0.203 in — Selected Type A (source footnote on this row)
• MS15795-808 — ØA 0.219 in — Selected Type A (source footnote on this row)
• MS15795-843 — ØA 0.594 in — Type B (source footnote on this row)
• MS15795-840 — ØA 0.604 in — Nonstandard (source footnote on this row)

Version status of the source

MS15795G is recorded as Canceled in the DLA ASSIST index, dated 2000-02-07, and is superseded by NASM15795. The dimensions on this page are the historical table of that document, which is what the USS and SAE names refer to in practice; they are not a list of current part numbers. Before ordering, confirm the equivalent current part number with your supplier.

What this table does not cover

Stated rather than filled in. Values that the source table does not print are not added here from trade catalogues.

• Only one table of the source is collected: the 58 rows of dash numbers 801 to 858. The same document has further tables for other materials, and their rows are not the same set, so no equivalence between them is claimed and they are not merged here.
• Large outside diameter fender washers are not covered: the source table collects selected sizes only, and for a small inside diameter it offers only a few large outside diameter options. The gap is stated, not filled with trade values.
• The type labels on this page come only from the footnotes the source printed on individual dash numbers. Most rows carry no footnote at all, so the table cannot be described as being all of one type, and an unmarked row is not turned into a type by inference.
• Narrow and wide are two outside diameters on the same inside diameter, both collected in the same source table; they are not two separate standards. USS and SAE are used here as the common industry names for the wide and the narrow pattern, and the labels Type A and Type B come from the source's own footnotes.
• Metric flat washers are a different system and are not interchangeable with US washers at the same nominal size; the metric family has its own chart on this site.
• Inch spring lock washers are outside this family: the table collects flat washers only.

Values on this page are compiled from the sources below; the calculated columns are worked out here.

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