Last updated 10 August 2026
About four times the per-side thickness on pitch diameter, against two times for a plain diameter. A 3/8-16 UNC-2A stud plated .0002 to .0005 per side has to be cut to .3279 / .3311 on pitch diameter.
A coating sits normal to the thread flank rather than parallel to the axis, so it shifts pitch diameter further than it shifts a flat surface. For a 60 degree form the rule of thumb every plating shop uses is four times the per-side thickness, and it appears in MIL-STD-870 and in Federal Screw Thread Specification H28.
This is the single most commonly missed number in the job, and it is missed by people who did the rest correctly: they doubled for sidedness, which is right, and had no reason to suspect a second factor of two was waiting. The symptom is a thread gauge that will not go after plating on a part whose major diameter checked fine.
| On the print | .3287 / .3331 in |
|---|---|
| Process | Plating |
| Per side | 0.0002 to 0.0005 in |
| The dimension gets | larger at this operation |
| Pitch diameter shift per unit of per-side effect | 4 times |
| Hold before the process | .3279 / .3311 in |
Open this case in the calculator, and change the numbers.
Computed by ctrlPlanner. MIL-STD-870, Federal Screw Thread Specification H28.