Parallel shaft gearheads and right angle gearheads with low ratios are generally not considered to be self locking. Right angle gearheads with ratios greater than 20:1 are often considered to be self locking. They will resist movement up to their torque rating. As the gearing nears the end of its useful life or if it is subjected to overload conditions, it may wear to the point where it is no longer self locking. Self locking gearing is not a recommended method for preventing movement in applications.