This is a Marbles Arms tang sight (aka Peep Sight) Henry Lever action rifle. This sight fits Big Boy 44 , 45, 357, 30/30 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 aproximately 2.000 TO 2.265 center to center, and the height adjustment is 1.920 ; TO 2.255; inches with an 18 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.