Metric threads with the rise of 1 mm/round are the most common.
Some time ago a 1.5mm rise was commonly used but the thread with the 1.0mm rise increase the contact surface as well as does not cut so deep as the 1.5mm.
Imperial threads
UNF (fine) correspond to the metric 1.5mm rise (1.27mm)
UNEF (Extra Fine) correspond to the metric 1mm rise (0.907mm)
Rifles with thin barrels can use 13×1 or ½x28 UNEF
The length of the thread is normally 15mm and shall be equipped with a groove closest to the edge (shoulder).
The thread shall also be beveled at the front so that the entry of the thread is protected.
