Early M1 production Narrow Base Gas Cylinder. These were produced at the Springfield Armory from approximately Summer 1942 or Rifle 300,00 to 1943 or Rifle 1.81M. They have flat on the top of the rear ring with a number or letter. They will also have a letter or number on the rear tang and in some cases both rear ring and tang will be marked. These are in good to very good condition, the bores have been gauge with a USGI Gage and are Good! They retain 99% of their new Dulite finish, come with their original Stacking Swivel and are beautiful. Good for the collector and shooter a like, get them while they last!!!