Pre-1975: This is an inside magazine tube for the Marlin model 99M1 & 75 rifles. It replaces Marlin part number 507422. It is 10 1/2" from the tip of the knurling to the end of the tube and 11 13/16" overall. It fits serial numbers that begin with 25 and up. These are made with a metal follower. Mfg: The Gun Garage SPECS: Made for pre 1975, model 75.