Step Drill Bit (4-12)

A step drill is a cone of steel machined into a series of concentric steps, each one a defined diameter with a cutting edge at its shoulder. You drill until the step you want has passed through the material, and stop. One bit therefore produces a whole range of hole sizes, and in thin material it does it better than a twist drill can.

Better, specifically, in three ways. A twist drill in thin sheet grabs as it breaks through and chews a triangular, out of round hole; a step drill cuts progressively and leaves a round one. A twist drill cannot safely enlarge an existing hole because there is nothing for its centre to bite on, so it snatches; a step drill sits in the existing hole on a smaller step and opens it out smoothly. And the shoulder of the next step deburrs the hole as it passes, so the edge comes out clean.

The limit is the other side of the same design, and it is absolute: this only works in SHEET. Each step is short, so the bit cannot drill deep. Thin steel, stainless sheet, trunking and enclosures, panel and box section wall, plastic and board are its materials. Solid bar and thick plate are not.

At 4 to 12mm this is the small electrical range: cable glands, small conduit entries, holes for switches and indicators in panel fronts, and general sheet work.

HSS, heat treated, with a titanium coating that reduces friction and heat, though it is microns thick and no substitute for a slow speed and a drop of cutting fluid.

Buyers are electricians and panel builders, air conditioning and ducting fitters, sheet metal workers, signage makers and hardware shops.

Ask on 94 77 111 8880 which range suits your gland sizes. Island-wide delivery.