This is a stainless steel magazine tube follower made for Marlin lever action rifles. This part has a concave divet in the face to accomodate pointed ammunition like Hornady Lever Evolution. Works with traditional style ammunition also.
This follower is for 30-30, .44 magnum, .45 Colt, .444 Marlin, and .35 remington.
For more information on the differences of Brass and Stainless followers click HERE