This is a brace that is inspired by the CAR15 stock. It fits a standard carbine length tube. The hardware recommended is a cap head M5 bolt 45mm OAL and a spring. The diameter of the head of the bolt needs to be less than 8mm. I used a hex head bolt that was oversized and just rounded it off by putting it in a drill and hitting it with a file. The spring is the generic hardware store spring roughly 8mm diameter, 30mm OAL uncompressed. Any similar sized pin or bolt should work.