Cored Holes For Threads
Cut threads: standard tolerances
Tapped holes require special diameters, depth, and draft to ensure production is cost effective. Draft may be retained, based on allowing 85% full thread depth at the small end and 55% at the large end. We recommend using a countersink or radius to provide relief for any displaced material and to strengthen the core in the tool.
Cut threads: critical tolerances
Greater dimensional accuracy is possible on tapped holes, but it comes at a higher cost. Draft may be retained, based on allowing 95% full thread depth at the small end and the maximum minor diameter at the large end.
Formed threads: critical tolerances
All formed threads require greater accuracy specified in these critical tolerances. Cored holes may be tapped without removing draft.
Pipe threads: standard tolerances
Cored holes are suitable for both NPT and ANPT. NPT should be specified where possible, due to the additional costs and steps required. The 1°47' taper per side is more important for ANPT than NPT.
No standards exist for metric pipe threads.