Abstract: A stackable, recessed, locking, insulated thumbscrew for connecting modules together in a stack such that removal of one module from the stack does not loosen other modules in the stack has an insulated knurled cap that fits over the end of a main screw body. The main screw body has an interior threaded end and an exterior threaded end, with the knurled cap slidable over the interior threaded end by means of a bayonet pin on the main screw body and corresponding bayonet slot in the knurled cap. A cap spring is captured between a retainer flange integral with or retainer ring mounted on the interior threaded end adjacent the exterior threaded end and the knurled cap to apply pressure to the knurled cap. In a raised position the knurled cap may be readily grasped for manual screwing and unscrewing of the thumbscrew to add or remove a module from the stack.