The adapter makes it possible to thread on most accessories threaded in 1/2x28 onto a standard M11 .380 barrel thread in 5/8x11. **This adapter has been machined with a short inner diameter, your .380 barrel tip must be cut back about .50" to fit and seat properly on this short adapter. **Will not seat on a standard M11 .380 barrel. Please call before ordering for details. We also offer a service for custom barrel cutting and fitting for this item. Finished in Black Oxide.