Depends. In most cases the tabs are indeed for pins. On my trade gun, there is a tab on the finial that is pinned and also 2 screws in the butt-plate. On others I have built, there is a tab (pin) and a screw in the butt-plate. In the trigger guard, the 2 tabs at the back end are pinned while the tang screw screws into the guard just forward of the bow (after removing the tab). You would need to get a good picture of the gun on which yours is modeled.
Black Hand