I hope this is as simple as I think it is. I have a part the calls out the true position of a 5/16-18 ID threaded hole with MMC. I think that the MMC should come off of the minor diameter. Onr of the owners and the QA manager think it should come off of the pitch diameter. Other than the fact we don't have a good way to measure the pitch diameter in house I think they are wrong. What are the prevailing winds on minor or pitch for MMC on a ID threaded hole?
Technically speaking: threaded holes per any spec have strict functional tolerances per that spec.
No further bonus allowance (aside from datum shift) should be permissible if the threads reference any thread specification (UN UNC UNF UNEF UNS etc).
For example, ANSI B1.1 (B1.3 for external threads) controls all UN spec-d threads. and particular for your 5/16-18 internal thread, all dims should be as follows:
(source is this handy engineers edge calculator)
Screw Threads Calculator for Internal Unified Inch Screw (engineersedge.com)
Technically speaking: threaded holes per any spec have strict functional tolerances per that spec.
No further bonus allowance (aside from datum shift) should be permissible if the threads reference any thread specification (UN UNC UNF UNEF UNS etc).
For example, ANSI B1.1 (B1.3 for external threads) controls all UN spec-d threads. and particular for your 5/16-18 internal thread, all dims should be as follows:
(source is this handy engineers edge calculator)
Screw Threads Calculator for Internal Unified Inch Screw (engineersedge.com)
kingsld1, have you ever put a piece with several bolts on a car, and found it won't go unless you just barely start all the fasteners first? That's a condition where the part only fits by the margin of thread clearance.
Meaningless to the final assembly, but not necessarily to the next stage in the build.