This is a Uncle Mike's Hammer Ext, model 2458-0.
This hammer extension fits All Marlin lever actions made in 1983 or later" including 39A" 39M" 1984" 1984C" 1985S 336C" 336T" 375" 444S and Glenfield 30A. Slips over hard-to-reach or hard-to-cock hammers for extra leverage.
Features:
Blued Steel
Knurled Surface
Allen Wrench Included
Fits Right or Left Side