These Barrel Tuners are a Brass, Rubber, and Stainless Steel 410 Construction. For tuning your rifle. The standard size is 30x1mm thread but other sizes can be made to suit your needs. F-Open Tuners weigh approximately 520 grams, and the smaller F-standard tuners weigh approximately 360 Grams however this changes with the thread diameter selected. They are held in location with a laser engraved locking ring allowing you to reference your adjustment positions. Your gunsmith will be required to thread your barrel for these tuners to be fitted. These tuners are proudly donated to the Australian FO team and fitted to many of the Teams rifles.