.177 Cal for the model 1377. Now you, the airgun hobbyist, can attach your favorite accessories to your .177 cal and .22 cal. airgun. This Steel Breech kit not only has a superior look, but it alleviates the need to purchase separate parts. With all-steel construction, it provides durability which in turn may improve your accuracy. With just the use of the two hex wrenches that are included and a flat-head screwdriver, this breech will be attached and ready for your accessories. Includes bolt and bolt handle.