A system for fastening two parts at abutting surfaces by forming an in-situ fastener. A device selectively forms variable width through holes on two parts to be fastened, such that the width of each through hole is larger on the first surface than the opposing second surface. Opposing first and second platens selectively urge the second surfaces of the two parts into engagement while the through holes of the two parts are in fluid communication with each other. An injection system includes a flow passage through the first platen to the through hole on the part engaged by the first platen, and a pressurizing mechanism for urging the flowable and hardenable material through the flow passage and into the first and second through holes between the first and second platens under pressure. Pressure is maintained while the flowable and hardenable material hardens within the through holes.