Drill bit shank A hex shank can be grasped by a 3-jaw drill chuck or held in a chuck specifically for hex shanks. Quarter-inch hex shanks are common for machine screwdriver bits and have spread from that application to be used for drill bits that are compatible with screwdriver machinery. The diameter of an SDS and SDS Plus shank is 10 millimeters. (The SDS Max is 18 millimeters.) The SDS shank has the advantage of fitting into a simple spring-loaded chuck, so that bits are simply pushed into the chuck without tightening. This shank and chucks made for it are especially suited to
Drill bit as the bit is either establishing the "center" of a hole or making a conical hole for a lathe "center". However, the true purpose of a center drill bit is the latter task, while the former task is best done with a "spotting drill bit" (as explained in detail below). Nevertheless, because of the frequent lumping together of both the terminology and the tool use, suppliers may call center drill bits "combined-drill-and-countersinks" in order to make it unambiguously clear what product is being ordered. They are numbered from 00 to 10 (smallest to largest). Center drill bits are meant to