The hammer track consists of several parts. The back plate is a piece of cold rolled 3/8" steel plate and is bolted to the 4"x"4"1/4" frame spacer. A piece of 1/4"x1.5" on each side of an aluminum spacer are bolted to the back plate and form a clamp for the ultra high molecular weight polyethylene [UHMWPE] "U" shaped hammer bushing. The cold rolled hammer back plate slides up and down in the UHMWPE bushing.
The UHMWPE "U" shaped bushing was supplied from McMaster-Carr pre machined to size. "Ultra high molecular weight polyethylene (UHMWPE) . . . is a very tough material, with the highest impact strength of any thermoplastic presently made. . . . It has a very low coefficient of friction, is self-lubricating, and is highly resistant to abrasion . . .in some forms being 15 times more resistant to abrasion than carbon steel. Its coefficient of friction is significantly lower than that of nylon and acetal, and is comparable to that of polytetrafluoroethylene (Teflon), but UHMWPE has better abrasion resistance than PTFE." (quotes from Wikipedia)