If you have a Briley Tube Set the bore size may be marked on the side of your tube set. Choke constrictions from Cylinder to Extra Full, in .005 inches (.127mm) increments let you precisely match your load to the shooting conditions. Choke site flush into the barrel, and choke features highly polished interior for less pellet deformation; reduced fliers and tighter patterns. Knurled grasping band speeds installation and removal. Our Vasco (VX), or All shot type thin wall chokes can handle all type shot, while the lead/bismuth only chokes are only suitable for lead and bismuth.