This 14mm threaded barrel adaptor is easily screwed into place at the muzzle of the Proline M40A3 Airsoft sniper rifle and allows the mounting of a barrel extension tube. The 14mm CCW threading fits most of the BETs out there and when used in combination with the front accessory rail it will transform the M40A3 into an M40A5 version. This adapter does not fit the Sportline M40A3.