# Trapezoidal lead screw

A lead screw as a plain envelope at its major diameter, axis along Z, centred on the origin. The thread is not modelled,
as in the library's threaded rods.

## Source

ISO 2904:2020, *ISO metric trapezoidal screw threads, basic dimensions*, Table 1, official preview
<https://cdn.standards.iteh.ai/samples/78729/7d158726108b478c889fa887d460ba78/ISO-2904-2020.pdf>:

| Size | d | P | Pitch diameter d2 | Minor diameter d3 |
|---|---|---|---|---|
| Tr8 × 1.5 | 8 | 1.5 | 7.25 | 6.2 |
| Tr10 × 2 | 10 | 2 | 9 | 7.5 |
| Tr12 × 3 | 12 | 3 | 10.5 | 8.5 |
| Tr16 × 4 | 16 | 4 | 14 | 11.5 |

Only d shapes this model. The T8 × 2, 4 and 8 and T10 × 4 screws are commercial multi-start designations that ISO 2904
doesn't tabulate: for those, d is the designation's nominal diameter. Lengths and leads come from the step.parts
catalogue metadata (MIT, `library/NOTICE.md`).