This is a Marble Arms tang sight (aka Peep Sight) Marlin 1894 (original 1894) and the 1893 lever action rifles. It comes with 3 different sight apertures (1/2 inch diameter with .055 hole; 1/2 inch diameter with .102 hole; 3/4 inch diameter with .032 hole). Hole spacing on the base of the sight is aprox 1.125 center to center, and the height adjustment is 1.920 inches to 2.255 inches at a 21 degree angle. Mounting screws are NOT INCLUDED with the tang sight, so if you need those screws they can be purchased in the option box below.