A shearable fastener has a threaded shank (10) adapted for engagement with a threaded bore and a head (12) formed for engagement with a drive tool. The shank (10) is formed with a series of axially separated weakenings (14) defining a series of shear planes, the weakenings (14) being formed such that the applied torque necessary to cause the shank (10) to shear increases progressively from the shear plane (14) furthest from the head (12) to the shear plane (14) nearest the head (12).