The self-locking of a helical worm gear depends, among other things, on the pitch angle of the gear, and the speed, type, and temperature of the lubricant. Self-locking increases with decreasing efficiency. A distinction of self-locking is made between static self-locking (Rs) and dynamic self-locking (Rd).
There are 3 ranges of self-locking:
A)     Self-locking is present when the efficiency is less than 0.45.
B)     Uncertain self-locking when the efficiency is between 0.45 and 0.55.
C)      There is no self-locking if the efficiency is greater than 0.55.