# Hex head screw, inch (ASME B18.2.1 / B18.6.3)

Hex head screw with Unified inch threads (UNC and UNF): hex cap screws to ASME B18.2.1 for 1/4 to 1/2 in, and hex head
machine screws to ASME B18.6.3 for #2 to #10, at any length. Presets cover the catalogue sizes.

## Geometry

Envelope for assemblies:

- hexagon head, width across flats **F**, height **H** (corner chamfers and the washer face are not modelled);
- plain shank at the basic major diameter **D**, length **L** (`length`, under the head); the thread is not modelled.

The head's bearing face is on the XY plane at the origin, the head above it, the shank along -Z; the hexagon's
corners point along X.

## Parameters

| Parameter | Meaning |
|---|---|
| `size` | Thread: #2 to #10 (hex head machine screws), 1/4 to 1/2 (hex cap screws), UNC and UNF |
| `length` | Nominal length L under the head, inches |
| `material` | `steel` (carbon steel, zinc plated), `stainless-18-8` (304), `stainless-316` |

## Sources

- **D**, basic major diameter: ASME B1.1-1989 (R2001), *Unified Inch Screw Threads*, external thread table, column
  "Major Diameter Basic", as reproduced at <https://www.engineersedge.com/screw_threads_chart.htm>.
- **#2 to #10**, hex head machine screws: ASME B18.6.3-2013, *Machine Screws, Tapping Screws, and Metallic Drive
  Screws (Inch Series)*, Table 29 (plain and slotted hex head screws, regular head): width across flats F **max** and
  head height H **max** (this table has no basic column). Read from Tanner Bolt's catalogue p. 72, which reproduces
  the ASME B18.6.3-2002 table with the same values (<https://www.tannerbolt.com/media/akeneo_connector/Machinehexhds.pdf>),
  checked against <https://torqbolt.com/asme-b18-6-3-plain-and-slotted-hexagon-head-machine-screws-dimensions-standards-specifications>.
  #0 is not a size of this table, so the catalogue's #0-80 hex head entries are left out.
- **1/4 to 1/2**, hex cap screws: ASME B18.2.1-2012, *Square, Hex, Heavy Hex, and Askew Head Bolts and Hex, Heavy Hex,
  Hex Flange, Lobed Head, and Lag Screws (Inch Series)*, Table 6 (hex cap screws): F **basic** and H **basic**, as
  reproduced at <https://torqbolt.com/asme-b18-2-1-hex-cap-screws-dimensions-standards-specifications> and
  <https://www.aftfasteners.com/hex-cap-screws-head-thread-dimensions-performance-mechanical-specs/>. The table number
  is from ASME's B18.2.1-2012 preview (<https://www.asme.org/getmedia/e6fec766-0f24-48db-b792-dc9a64a5b325/34661.pdf>).

The machine screw rows use max values and the cap screw rows basic values because those are the columns each table
gives. Inch values as printed in the tables; the model converts them to millimetres (1 in = 25.4 mm).

| Size | D | F | H |
|---|---|---|---|
| #2 | 0.086 | 0.125 | 0.05 |
| #4 | 0.112 | 0.188 | 0.06 |
| #6 | 0.138 | 0.25 | 0.093 |
| #8 | 0.164 | 0.25 | 0.11 |
| #10 | 0.19 | 0.312 | 0.12 |
| 1/4 | 0.25 | 0.4375 | 0.15625 |
| 5/16 | 0.3125 | 0.5 | 0.203125 |
| 3/8 | 0.375 | 0.5625 | 0.234375 |
| 7/16 | 0.4375 | 0.625 | 0.28125 |
| 1/2 | 0.5 | 0.75 | 0.3125 |

Corrected in this audit: #4 F 0.1875 -> 0.188 and #10 F 0.3125 -> 0.312 (the table's printed max values).

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