2-1/4" X 1/2" Pilot Hole HSS Straight Shank Counterbore BoltsandNuts.com Drill Size: 1-7/64"

Drill Size: 1-7/64"

Part Number SDS4F9166

The blades are hardened to 58 - 64 HRC

and 10 inch impact extensions

Part Number DWTSH2-1/4-8

2-1/4" X 1/2" Pilot Hole HSS Straight Shank Counterbore BoltsandNuts.com Drill Size: 1-7/64"Product Description Counterboring is the enlargement of a portion of a hole that has previously been formed. If the counterbored portion is shallow (1 8" or less), the operations is usually known as spot facing; for example, a flat seat for a bolt head or nut. If, on the other hand, the hole is enlarged to a considerable depth, it is designated as counterboring. These counterbores are made of two piece construction, having an integral shank and