Back-boring reamers are invaluable for all shops that do shotgun work, especially choke and barrel modifications. Reamers available in .005″ increments from .725″ to .740″ in 12 gauge. Lead angle of reamer matches the angle of most chokes to blend into an existing choke. Many possible uses. Shortened barrels may be back-bored to within 2″ to 3″ of muzzle to provide a degree of constriction or “choke” in what would otherwise be a cylinder bore barrel. A choked barrel can be back-bored to enlarge the bore to provide “extra” constriction for competitive shooters. For rough pitted bores, these reamers provide an effective and efficient means of Mfg: Clymer SPECS: Reamers 5″ (12.7cm) long. Made of M-7 high speed steel, hardened and drawn. Advise Reamer Stock # from chart.