Muzzle break thread protector for standard 1/2″ UNF threads.

16mm outer diameter so is a flush fit with 16mm OD barrels such as:
BSA Ultra
BSA Ultra SE
BSA Ultramax
BSA Ultra XL
BSA Ultra CLX
BSA Scorpion
BSA Scorpion SE
Gamo Phox
Gamo Coyote
Gamo Urban
Gamo Chacal
Gamo Dynamax
Gamo GX40
Gamo HPA
Gamo Venari