first

second

third

none of these

a taper key which fits half in the key way of hub and half in the key way of shaft

a taper key which fits in a key way of the hub and is flat on the shaft

a taper key which fits in a key way of the hub and the bottom of the key is shaped to fit the curved surface of the shaft

provided in pairs at right angles and each key is to withstand torsion in one direction only

plasticity

elasticity

ductility

malleability

in decreasing the slip of the belt

in increasing the slip of the belt

to keep the belt in centre on a pulley while it is in motion

to increase pulley life

50 Degree Centigrade above upper critical temperature

50 Degree Centigrade below upper critical temperature

50 Degree Centigrade above lower critical temperature

50 Degree Centigrade below lower critical temperature