This is a XS Sights Sight known as the Ghost Ring Rear, model ML-0012-5.
The XS Ghost Ring WS hunting sights offer improved accuracy and faster sight acquisition in a rugged all-steel design. Fits Marlin 336" 1894" & 30AS with existing front sight blade and ramp that is screwed onto the barrel. Does not fit models with front sight blade dovetailed directly into the barrel. Precision machined in Fort Worth" TX. XS Ghost Ring WS is fully adjustable for windage and elevation and comes with two apertures" .230" and .191" inside diameter" for different lighting conditions. The large Ghost Ring affords great field of view for fast target acquisition. The XS White Stripe (WS) front sight replaces the existing blade and ramp and features a blued steel body with a painted white stripe face. White on black front post is highly visible in all lighting conditions" as well as provides contrast against any color background. Due to moving the rear sight from the barrel to the receiver" some zeroing issues might arise. Alternate front sight heights are available and covered under XS' No Questions Asked Warranty.
Features:
White stripe front
Ghost ring rear
Hunting sights
