the tapered segments 44 of the resin compression layer 42 compress the resin 60 between the exterior of the mine roof bolt 10 and the bore hole wall the expansion assembly 32 may include a stop mechanism that resists relative rotation between the bolt 10 and the plug 40 until a torque in excess of a predetermined torque is applied to the drive end 22 of the bolt 10 at this torque the resistance offered by the curing resin 60 to rotation of the plug 40 fractures the stop mechanism when the torque for breaking the stop mechanism is reached resin mixing is complete and the plug 40 travels downwardly into the expansion shell 34 in this manner expansion of the shell 34 is delayed until the resin 60 is mixed but not after the resin 60 completely rigidifies in the bore hole 12 the stop mechanism includes any suitable device that restrains axial movement of the plug 40 on the bolt 10 beyond a pre selected point on the threaded end 18 of the bolt 10 such as a breakable obstruction member e g a shear pin suitably retained within the plug 40 the resin compression layer 42 serves several functions.