This is a .310 High Speed Steel (HSS) reamer with a 3/4-inch long .248 pilot. This is a USA-made reamer modified for small engine applications.

Piloted reamers are primarily used for machining the valve guide counter bore to accept oversize replacement valve guides.  This a common procedure in small racing engines; in most cases, engine builders replace factory guides with a better quality bronze alloy type material. These reamers have a .248 pilot and would be used most often when working with a 1/4-inch stem valve. The guide counter bore is usually machined .002 under replacement valve guide diameter.

Caution should be used to ensure that counter bore material is a softer machinable material. Bronze alloys are much harder and would require a reamer made with carbide.

These reamers should be used at a slower RPM range (approximately 600 or less). We recommend using a heavy dark cutting fluid. This type of cutting fluid can be found at any plumbing supply or big box hardware store and is referred to as pipe tapping or thread cutting oil with a Sulfur blend.

Upper reamer centering guides for some applications are available separately.