Router BitsTerminology

Cutting Diameter ('D') refers to the largest cutting diameter of the tool and is represented in fractions, decimals and/or millimeters.

Cutting Length ('B or C') refers to the length or 'depth' of the cutting edge. This dimension usually represents the cutting edge
length parallel to the length of the shank. Represented in fractions and/or millimeters.

Shank Diameter ('d') refers to the largest diameter of the shank and is equivalent to the router collet inside diameter that is necessary to use the tool. This dimension is represented in fractions.

Overall Length ('L') refers to the total length of a router bit from the top of the shank to the bottom of the tool at its furthestmost point. This dimension is represented in fractions and/or millimeters.

Radius ('R') of a cutting tool edge refers to one-half the diameter of a complete circle, and is shown in fractions and/or millimeters.

Bevel Angle ('a°') refers to the angle formed between the cutting tool edge and a straight line drawn parallel or perpendicular to the shank length, and is measured in degrees.

Rake Angle ('T') refers to the angle (or 'hook') of the cutting tool tip in relationship to a straight line drawn perpendicular through the center of the tool. This dimension is measured in degrees.

Primary Radial Clearance ('P') refers to the relief grind on the tip of the tool and is measured in degrees.

Secondary Radial Clearance('O') refers to the combined relief grind of the primary clearance and the clearance ground into the
body of the tool. This dimension is measured in degrees.

Penetration Clearance ('S') refers to the angle formed between the cutting tool edge and a straight line drawn perpendicular to the shank of the tool, and is measured in degrees. This angle allows gradual penetration into the material.

Web Diameter ('N') refers to the thickness of the ground steel body of the tool, including the heel area ('M'). The web must be of adequate thickness to withstand industrial routing applications.