The RE-A5 receiver extension tube is designed to work with the Vltor A5 Rifle Recoil System. Physically, the A5 tube is slightly longer than a traditional AR-15 receiver extension tube, the A5 tube has seven locking positions and is designed to work with a MilSpec diameter, lengthened collapsable stock, such as the Vltor Enhanced Modstock.
If you are using the A5 tube as part of the Vltor A5 Recoil System on an AR-15 type rifle or carbine, it must be used in conjunction with a Vltor A5 Buffer & Spring. These parts are NOT the same as standard carbine or rifle receiver extensions or buffers.
Attempting to use these parts with standard carbine or rifle recoil systems will result in damage to the firearm!