A more realistic rocket engine tail cone than the ones included in Estes kits.
It's scaled to fit an Estes BT-60, which has an inside diameter of 1.595 inches. It should slide in easily, but that may depend on your printer.
Make sure the end of the motor tube is fairly close to the bottom of the nozzle so it isn't exposed to too much heat.
Prints without support; as long as you have decent bed adhesion you shouldn't need a raft or brim.