This standard establishes the general dimensions of long machine taps for ISO metric triangular profile threads. It is valid for taps with a nominal diameter from 3 to 24 mm and essentially applies to taps with a relief shank intended for making ISO metric threads with a triangular profile:
——coarse pitch (see point 3);
——fine pitch (see point 4). The threaded lengths of these taps comply with those of UNI 7457 regarding short machine and hand taps with normal shank. The lengths of the shanks are increased by 50% in relation to those established in UNI 7457; the total lengths therefore vary in proportion. In the case of using taps with a nominal diameter greater than 24 mm, the threaded length must be that established, for the same diameter, by UNI 7457 and the length of the tang (L —/j ) must be increased by 50%.
UNI 7649-1977 history
1977UNI 7649-1977 Long machine taps for ISO metric threads with triangular cross-section