Williams Gun Sight Corporations receiver sight with target knobs for the Marlin centerfire lever action models, uses two rear scope mount holes. Model 1894 requires hammer extension. Internal micrometer adjustments have positive click adjustments. Comes with one 3/8″ diameter knurled aperture with a .093″ peep. The FP is strong, rugged and dependable. The blue- black anodizing produces a long lasting no rust finish. The alloy used to manufacture this sight has a tensile strength of 85,000 pounds. Yet, the FP is light and compact weighing only 1 1/2 ounces. Many rifles are now being drilled and tapped at the factory for installation of the FP. Please be aware that some rifles may require drilling and tapping for installation.