# Inch lock washers (ASME B18.21.1)

Regular helical spring lock washers (split) and external tooth lock washers for inch screws #2 to 1/2. Presets
cover the catalogue's inch split and external-tooth lock washers.

## Geometry

Envelope for assemblies: the flat blank, an annulus from the minimum inside diameter **d** to the maximum outside
diameter **dc**, as thick as the section (split: **h**, the minimum mean section thickness; tooth: **t** max), lying on
the XY plane, centred on the origin. The tables do not dimension the split washer's helix or gap, nor the tooth
washer's teeth (count, shape, twist), so neither is modelled. The model is in millimetres (1 in = 25.4 mm).

## Parameters

| Parameter | Meaning |
|---|---|
| `size` | Screw size, #2 to 1/2 |
| `style` | `split` (regular helical spring lock washer) or `tooth` (external tooth lock washer) |
| `material` | `steel` or `stainless-18-8` (304) |

## Sources

- ASME B18.21.1-2009 (R2016), *Washers: Helical Spring-Lock, Tooth Lock, and Plain Washers (Inch Series)*,
  **Table 1** "Regular Helical Spring-Lock Washers" (reproduction consulted:
  https://www.globalfastener.com/standards/detail_22194.html) and the **External Tooth-Lock Washers** table
  (https://www.globalfastener.com/standards/detail_22201.html; it starts at #3).
- #2 external tooth: ASME B18.21.1-1999 as reproduced by Aspen Fasteners, "External Tooth Lock Washers ASME
  B18.21.1-1999", p. 2 (https://www.aspenfasteners.com/content/pdf/external_tooth_lockwasher_specification.pdf),
  whose values for #3 to 1/2 are the same as the 2009 table's.

Inches:

| Size | Split d min | Split dc max | Split h min | Tooth d min | Tooth dc max | Tooth t max |
|---|---|---|---|---|---|---|
| #2 | .088 | .172 | .020 | .086 | .189 | .013 |
| #4 | .114 | .209 | .025 | .115 | .260 | .018 |
| #6 | .141 | .250 | .031 | .141 | .320 | .022 |
| #8 | .167 | .293 | .040 | .168 | .381 | .023 |
| #10 | .193 | .334 | .047 | .195 | .410 | .024 |
| 1/4 | .252 | .487 | .062 | .256 | .510 | .028 |
| 5/16 | .314 | .583 | .078 | .320 | .610 | .034 |
| 3/8 | .377 | .680 | .094 | .384 | .694 | .040 |
| 1/2 | .502 | .869 | .125 | .513 | .900 | .045 |

Not covered: #0 (in neither table).

Preset list: sizes of the step.parts catalogue (MIT), see `library/NOTICE.md`.