# Flat head socket cap screw, inch (ASME B18.3)

Flat (82° countersunk) head socket cap screw, Unified inch threads (UNC and UNF) #0-80 to 1/2-20, at any length.
Presets cover the catalogue sizes.

## Geometry

Envelope for assemblies:

- 82° countersunk head of diameter **A** (theoretical sharp, max); its height follows from the head angle,
  (A - D) / 2 / tan 41°, which is the table's reference head height;
- hexagon socket, nominal key size **J**, depth **T** (key engagement, min);
- plain shank at the basic major diameter **D**; the thread is not modelled.

The head's top face is on the XY plane at the origin and the screw points along -Z. `length` is the **overall**
length L (head included), as flat head screws are specified.

## Parameters

| Parameter | Meaning |
|---|---|
| `size` | Thread, #0-80 to 1/2-20 (UNC and UNF) |
| `length` | Nominal overall length L, inches |
| `material` | `steel` (alloy steel, black oxide), `stainless-18-8` (304), `stainless-316` |

## Sources

- **D**, basic major diameter (ASME B1.1): NBS Handbook H28 (1969) Part I, Table 2.7 "Unified standard screw thread
  series", column "Nominal size and basic major diameter" (printed p. 2.08,
  <https://nvlpubs.nist.gov/nistpubs/Legacy/hb/nbshandbook28-1969p1.pdf>); the same basic diameters head the B18.3
  tables below.
- **A (theoretical sharp, max), J, T min, head angle 82°**: ASME B18.3-2012, Table 8 (hexagon socket flat countersunk
  head cap screws), as reproduced at <https://www.globalfastener.com/standards/detail_20306.html> (head angle 82° ±2°);
  the same values in ASME B18.3-2003 Table 2A (<https://www.fasten.it/en/norms/norm/asme_b18.3_table_2a>), in
  Holo-Krome's *Technical Manual* (2015) Table 8, p. 10 (<https://holo-krome.com/uploads/7/2/7/5/72754089/hk_consolidated_tech_manual_full_2015.pdf>) and in Unbrako's *Engineering Guide*, p. 14
  (<https://wp.optics.arizona.edu/optomech/wp-content/uploads/sites/53/2016/08/UnBrako-fasteners.pdf>; it prints 1/2 A as .937, every other source .938).

The values are the same in the 2003 and 2012 editions; the recipe cites ASME B18.3-2012. Inch values as in the standard; the model converts them to millimetres (1 in = 25.4 mm).

| Size | D | A | J | T |
|---|---|---|---|---|
| #0 | 0.06 | 0.138 | 0.035 | 0.025 |
| #1 | 0.073 | 0.168 | 0.05 | 0.031 |
| #2 | 0.086 | 0.197 | 0.05 | 0.038 |
| #3 | 0.099 | 0.226 | 0.0625 | 0.044 |
| #4 | 0.112 | 0.255 | 0.0625 | 0.055 |
| #5 | 0.125 | 0.281 | 0.078125 | 0.061 |
| #6 | 0.138 | 0.307 | 0.078125 | 0.066 |
| #8 | 0.164 | 0.359 | 0.09375 | 0.076 |
| #10 | 0.19 | 0.411 | 0.125 | 0.087 |
| 1/4 | 0.25 | 0.531 | 0.15625 | 0.111 |
| 5/16 | 0.3125 | 0.656 | 0.1875 | 0.135 |
| 3/8 | 0.375 | 0.781 | 0.21875 | 0.159 |
| 7/16 | 0.4375 | 0.844 | 0.25 | 0.159 |
| 1/2 | 0.5 | 0.938 | 0.3125 | 0.172 |

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