Compensator for reduced recoil. May require fitting. Fits K40 only. ****NOTE: These barrels will not fit older framed models that have not been updated. This update service is available through the service department at a cost of $190 + $25 s&h....If you are unsure of the age of your pistol, or wish to have this service performed, please contact the Gun Tech. Support & Service / Repair department.