THREAD DEPTH
The american standard for unified threads is very similar to the American national standard with certain modifications. The thread forms are practically the same and the basic 60-degree angle is the same. The depth of an external American national thread is 6495 x pitch. The constant for American national thread depth may be rounded off from .6495 to .65 , and theconstant for unified thread depth may be rounded to .613 the thread deoyh and the root truncation(tool flat) of American national thread is fixed or definite, but these factors are variable within limits for unifieds. A rounded root for unified threads is desirable whether from tool wear or by design. A rounded crest is also desirable but not required. The constants .613 for thread depth and .125 for the flat on the end of the tool were selected for calculations on unified threads in this unit.