A twist-drivable pin assembly includes first and second drivers, each having a driving end which can be received in a bore 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 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 formed in it. Each of first and second twist-drivable pins has a bore 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.
