インチねじ

インチねじの設計ガイドライン

はめあい等級（公差）：
Class 2A/2B: The industrial standard. Allows for plating buildup and easy assembly.
Class 3A/3B: Zero clearance fit. Used for high-precision applications. ヒント: Do not specify Class 3 if you plan to plate the part heavily, or the screw won’t fit.

Plating Allowance:
Imperial threads are often plated (Zinc/Cadmium). Plating adds thickness (4x the plating thickness on the pitch diameter). ヒント: We machine “pre-plate” threads slightly undersized (external) or oversized (internal) to accommodate the coating.

TPI vs. Pitch:
Remember that Imperial threads are defined by “Threads Per Inch” (TPI), not the distance between threads. A higher number means a finer thread (opposite of metric).

UNJ Root Radius:
If designing for Aerospace, ensure you specify UNJ (e.g., UNJF). This requires us to use specialized inserts with a larger nose radius. A standard UN tool will create a stress riser that can fail certification.