Bayonet connection key includes upper and lower blocks shaped to be inserted one at a time into a key space, having laterally spaced apart upper and lower flat first and second side contact surfaces, and means for retaining blocks against each other. Bolt or screw may be disposed through an aperture in retaining plate and screwed into threaded hole in upper block pressing retaining plate against lower block. Upper block may include axially spaced apart upwardly extending forward and aft lugs, aft lug shorter than forward lug, and inwardly extending upper stop lug at aft end of upper block. Alternatively bendable tab extending axially forward from a front end of the lower block may be bent up contacting upper block for retaining blocks in key space. Upper block may include forward and aft lugs of same radial length and inwardly extending stop lug at aft end of lower block.