# Plain washer, inch (ASME B18.21.1 / B18.22.1 Type A) Type A plain washer for inch screws, narrow series N (the "SAE" washer) and wide series W (the "USS" washer), #0 to 1/2 in; and fender washers (F) for #0 to 1/2 in screws. Presets cover the catalogue's flat washers (the narrow washer for each screw size) and its fender washers. ## Geometry A flat ring at the table's nominal inside diameter **ID**, outside diameter **OD** and thickness **T**. It sits on the XY plane, centred on the origin. ## Parameters | Parameter | Meaning | |---|---| | `size` | Screw size and series: `1/4 N` (narrow, SAE), `1/4 W` (wide, USS), ...; `#0` to `#10` have one series; `#0 F` to `1/2 F` fender washers | | `material` | `steel` (carbon steel, zinc plated), `stainless-18-8` (304), `stainless-316` | ## Source Type A plain washers, preferred sizes: inside diameter, outside diameter and thickness, basic values. - ASME B18.21.1-2009 (R2016), *Washers: Helical Spring-Lock, Tooth Lock, and Plain Washers (Inch Series)*, Type A plain washers, preferred sizes, as reproduced at . This edition names the three smallest rows No. 0, No. 2 and No. 4. - The same values in ANSI/ASME B18.22.1-1965 (R1998), *Plain Washers*, Table 1A: , (that edition leaves the size column of the 0.078, 0.094 and 0.125 in rows blank). - B18.22.1 was consolidated into B18.21.1 (ASME: ). The presets name ASME B18.22.1, the designation the catalogue uses; the values are those of both editions. Inch values as in the table; the model converts them to millimetres (1 in = 25.4 mm). | Size | ID | OD | T | |---|---|---|---| | #0 | 0.078 | 0.188 | 0.020 | | #2 | 0.094 | 0.250 | 0.020 | | #4 | 0.125 | 0.312 | 0.032 | | #6 | 0.156 | 0.375 | 0.049 | | #8 | 0.188 | 0.438 | 0.049 | | #10 | 0.219 | 0.500 | 0.049 | | 1/4 N | 0.281 | 0.625 | 0.065 | | 1/4 W | 0.312 | 0.734 | 0.065 | | 5/16 N | 0.344 | 0.688 | 0.065 | | 5/16 W | 0.375 | 0.875 | 0.083 | | 3/8 N | 0.406 | 0.812 | 0.065 | | 3/8 W | 0.438 | 1.000 | 0.083 | | 7/16 N | 0.469 | 0.922 | 0.065 | | 7/16 W | 0.500 | 1.250 | 0.083 | | 1/2 N | 0.531 | 1.062 | 0.095 | | 1/2 W | 0.562 | 1.375 | 0.109 | Changed in this audit: the sizes "#2 (3/32)" and "#4 (1/8)" are now "#2" and "#4" (the B18.21.1-2009 names; "3/32" and "1/8" were in no source), and the No. 0 row (#0 screws) was added from the same table. ## Sources: fender washers No standard covers fender washers, and suppliers sell several outside diameters and thicknesses for each screw size. **The fender sizes' geometry was measured from the published reference models** below (each model's bore and outside cylinder radii and its thickness, read from its faces) and is checked preset by preset against them (bounding box within 0.05 mm, volume within 2 %). - **step.parts**, `asme_fender_washer__simple` for #0-80 to 1/2-13 (https://www.step.parts, repository https://github.com/earthtojake/step.parts, commit c6113328, `catalog/step/`): step.parts' own "analytic simplified" models, original project material under the repository's **MIT** licence (© 2026 earthtojake). The models are proportional to the screw's nominal diameter d: OD 3.2 d, ID 1.08 d, T 0.18 d (at least 0.45 mm). Note that ID 1.08 d is a close clearance; check a supplier's washer where the fit matters. The catalogue's 5/16-24, 3/8-24 and 1/2-20 fender models are drawn for a 1/8 in screw (OD 0.4 in, bore smaller than the named screw) and are not presets. Size, mm: | Size | ID | OD | T | |---|---|---|---| | #0 F | 1.646 | 4.8768 | 0.45 | | #2 F | 2.3592 | 6.9901 | 0.45 | | #4 F | 3.0724 | 9.1034 | 0.5121 | | #6 F | 3.7856 | 11.2166 | 0.6309 | | #8 F | 4.4988 | 13.3299 | 0.7498 | | #10 F | 5.212 | 15.4432 | 0.8687 | | 1/4 F | 6.858 | 20.32 | 1.143 | | 5/16 F | 8.5724 | 25.4 | 1.4287 | | 3/8 F | 10.287 | 30.48 | 1.7145 | | 1/2 F | 13.716 | 40.64 | 2.286 | Preset list: sizes of the step.parts catalogue (MIT), see `library/NOTICE.md`.