be across threaded portion of shank

be parallel to axis of bolt

be normal to threaded portion of shank

never be across the threaded portion

one smaller nut is tightened over main nut and main nut tightened against smaller one by loosening, creating friction jamming

a slot is cut partly is middle of nut and then slot reduced by tightening a screw

a hard fiber or nylon cotter is recessed in the nut and becomes threaded as the nut is screwed on the bolt causing a tight grip

through slots are made at top and a cotter pin is passed through these and a hole in the bolt, and cotter pin spitted and bent in reverse direction at other end

compression

tension

shear

combined loads

to produce torque

for speed reduction

to obtain variable speeds

to increase efficiency of system

reducing stress concentration

ease of manufacture

safety

fullering and caulking