Design specificationsIntermediate
Thread Fit and Tolerance Design
Metric thread classes, hole prep, and when to add thread locking or inserts.
Mechanical DFM2024-11-1113 min read7,0124.8
Summary
Specify thread class (6H/6g) and depth. For plastics and soft alloys, use heat-set inserts or coil inserts for durability.
1Metric classes
6H internal / 6g external is the default clearance fit for general assemblies.
2Hole prep
Tap drill sizes per ISO tables; blind holes need chip evacuation space.
3Inserts
Use brass or helical inserts in plastic and thin-wall aluminum for repeated assembly.
Key points
- Default 6H/6g for general use
- Inserts in plastic threads
- Allow depth for tap chips
ThreadsTolerancesDFM
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