A surgical tool system including a handpiece with a motor and a cutting accessory with a shaft that is rotated by the handpiece motor. The handpiece includes a coupling assembly with plural locking elements for holding the accessory shaft to an output drive shaft that is actuated by the handpiece motor. The locking elements are longitudinally spaced apart from each other. The accessory shaft is formed with retention features against which the handpiece locking elements engage. The shaft retention features are in columns. The retention features in adjacent retention features are longitudinally offset from each other. This allows the coarse or fine adjustment of the extent to which the accessory shaft extends forward from the handpiece coupling assembly.
