I'm having a hard time finding the correct sling mount/swivels for my sons rem. 870 youth model. The Uncle Mikes that I bougth has a small 'bolt' that should screw into the magazine on the shotgun, but apparently I need the whole piece that screws onto the end of the mag tube for the youth model 20 ga. Any help on exactly what I need & where I can get it from is greatly appreciated!