2.5mm Wall .625 Cal Tactical Mounting Rail System By Venom Blowguns&trade; Compatible with Cold Steel Professional&trade; and Venom Blowguns&trade; 2.5mm Wall Blowguns Tactical MOUNTING RAIL FOR 2.5MM WALL BLOWGUNS. Picatinny and Weaver Compatible Slides onto .625 PROFESSIONAL 2.5mm Wall Blowguns, will not fit 1.5mm MAGNUM Models IF YOUR TUBE IS THE SIZE OF A PENNY YOU HAVE A 1.5MM WALL BLOWGUN IF YOUR TUBE IS THE SIZE OF A NICKEL YOU HAVE A 2.5MM WALL BLOWGUN Please be careful in your sizing and best to order only if you have your blowgun in front of you to check sizing