A twist-drivable pin assembly includes first and second drivers, each having a driving end (2) which can be received in a bore (104) in the end of a twist-drivable pin, and an opposite end at which torque can be applied. The cross-sectional shape of each of the drivers at its driving end has a first plurality of apexes (18) whose relative locations coincide with the apexes of a regular polygon such as a hexagon. The drivers differ from one another in their cross-sectional shapes at the driving end by virtue of one or more faces of at least one of the drivers between adjacent pairs of apexes having a groove (20) formed in it. Each of first and second twist-drivable pins has a bore (64) extending into it which is defined by a second plurality of apexes arranged as a regular polygon such as a hexagon and which is open at one end. The number of apexes of the second plurality is equal to the number of apexes of the first plurality. The first and second pins differ from one another by virtue of markings associated with the open ends of the polygonal bores. The shape defined by the markings corresponds to the cross-sectional shape of a corresponding one of the first and second drivers.
