DEMO — fictional range. Local brief only, NOT SENT. No personal data is collected or transmitted.
FINISH
Plating is applied after the thread is cut.
Every coating adds thickness, and on a threaded part that thickness is added to the feature that has to fit. The finish and the thread class have to be specified together.
- As machined
- Tool marks left as cut · the cheapest option and honest about what it is
- Zinc plated
- For steel · protection that is consumed over time rather than permanent
- Nickel plated
- For brass and steel · hard, decorative, changes the thread more than zinc
- Oxide
- For iron and steel · a thin conversion coating, minimal dimensional change
- Anodised
- For aluminium · build-up is significant on a thread, and it is hard
- Passivated
- For stainless · removes free iron, changes nothing dimensionally
Illustrative finish reference
| Finish | Typical use | Build-up on a thread |
|---|---|---|
| As machined | Hidden internal parts | None |
| Oxide | Iron and steel parts | Negligible |
| Zinc plated | Steel fasteners | Measurable |
| Anodised | Aluminium that is handled | Significant |
Why the thread is usually gauged before plating.
Because gauging after plating measures the coating as much as the thread. The useful arrangement is to gauge before plating to a class that allows for the coating, and to say so on the drawing.
The one worth avoiding.
A tight thread class and a thick coating on the same part. The two specifications are individually reasonable and together they produce a part that will not assemble.