The outer diameter is 19 mm you can install a 19 mm diameter decoration front tube. This kits is only for Worker Mod Prophecy Power Type Short Dart SetNeed to match Worker Mod 312mm Aluminum Alloy Tube Kits. Manufacturered by WORKER. All parts are separateand the product included small parts you need to install and assemble your blasterPlease be careful installing the parts to avoid damage to your Blaster! Blaster not included! Compatible with Nerf Retaliator with Worker Mod Prophecy Power Type Short Dart Set with Worker Mod 312mm Aluminum Alloy Tube.