X-Barrel & STX barrel liner lock connection, as used on the FX Impact-X, Impact MK2, Impact M3, Impact M4, Wildcat MK2, MK3, Dreamline, DRS, King, Panthera, Dynamic, Maverick and Crown / Crown MK2 air rifles. (Not used on Superlight barrels)

.177 (4.5mm) – 19968
.22 (5.5mm) – 19969
.25 (6.25mm) – 19970
.30 (7.62mm) – 19971