Pitch diameter, functional diameter Per ASME B1.7-2006 Definitions [ back to main page ]
Pitch diameter, functional diameter: the pitch diameter of the enveloping thread of perfect pitch, lead, and flank angles, having full depth of engagement, but clear at the crests, and of a specified length of engagement. Design pitch diameter of the enveloping thread is equal to that of the product maximum material limit. Functional diameter may be derived by adding to the pitch diameter in the case of an external thread, or subtracting from the pitch diameter in the case of an internal thread. It is the cumulative effects of variation from specified profile, including variations in lead and flank angles over a specified length of engagement. The effects of taper, out-of roundness, and surface defects may be positive or negative on either external or internal threads. The term functional diameter refers to the GO functional diameter. GO thread gages are used to inspect / evaluate GO functional diameters. Virtual diameter, effective size, virtual effective diameter, and thread assembly diameter are defined the same as the preferred term functional diameter.
Original Posting: 3/20/2012
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