Honing and fitting valve guides is a difficult and time-consuming job. With these Kibblewhite reamers you will ream a valve guide to exact dimension without any taper in 4 to 5 seconds only. Guides will last longer than with the honing method because there is no crosshatch left after reaming. One size allows you to fit both intake & exhaust if you use Kibblewhite valves & guides. These reamers are for Manganese bronze only, do not use with cast iron guides.