An extension is a piece of archery equipment that connects to the riser (main part of the bow) and the stabilizer system. It is used to move the V bars (left and right) stabilizers further from the grip, and changes the balance of the bow, and the feel of the shot.
This part is commonly made of aluminum or carbon fiber. I have had two carbon fiber parts 'explode' on me, and the second incident almost cost me an elimination match (but not quite). I decided to fabricate an aluminum one to prevent this from every happening again.
I turned this part manually, with groves on either end of a knurled section to aid in tightening it down to my bow. I also turned Delrin plugs that press-fit into the part and hold in a rubber dampening core. The rubber O-rings also provide damping, and help with grip. Finally, I permanently fixed a 5/16"-24 threaded rod to one end to mate with the corresponding bushing on the Riser.
Using my custom equipment at Collegiate nationals (and many other tournaments)