pulley is made the weakest

key is made the weakest

key is made the stongest

all the three are designed for equal strength

4 mm

5 mm

6 mm

7 mm

knuckle joint

cotter joint

oldham coupling

universal joint

only to the pinion

only to the gear

to stronger of the pinion or gear

to weaker of the pinion or gear

threads for the nut at one end and head at the other end

head at one end and the other end fits into a tapped hole of one of the parts to be fastened

threads at both ends

pointed threads