How to Measure the Minor Diameter of Internal Threads

[Wayne]

Re: Proper Thread Measurement

… an undersized minor diameter would not affect if not enhance the thread strength….

An undersized minor diameter of an internal thread may interfere with the mating part causing assembly difficulty, galling or some other damage to the threaded connection. Any additional strength gained by leaving the tiny amount of material in place could be mitigated by the damage to the connection.

 

[Gordon Clarke]

Re: Proper Thread Measurement

An undersized minor diameter of an internal thread may interfere with the mating part causing assembly difficulty, galling or some other damage to the threaded connection. Any additional strength gained by leaving the tiny amount of material in place could be mitigated by the damage to the connection.

I'm definately with Wayne on this one. A good finish on the minor diameter (bore diameter) is either a radius or a flat. A sharp V should be avoided and only really exists in theory. The minor diameter on an internal thread is almost always the diameter with the greatest tolerance so why create an unnecessary problem? The thread cutting tool will also last longer the larger the diameter is made on the minor diameter while of course still staying within tolerance.