Metallics BHDM6 Bell Hanger Drill Bit Dia 5/16" 18" Carb tip Fish Hole (1pc)

The BHDM6 is a 5/16 inch diameter bell hanger bit with an 18 inch overall length, so it will bore a 5/16 inch hole and pass through built-up framing, sill plates, and masonry walls up to roughly the usable flute length of that 18 inch shank. Carbide tipped, which is what lets it take brick, block, and nail-embedded wood without burning up.

The fish hole is the eye drilled through the shank near the tip. After you bore the hole, you thread your wire or pull string through the eye and back the bit out, dragging the wire through with it. That saves a second trip with a fish tape, which is the whole reason low voltage and electrical installers use a bell hanger bit instead of a standard twist bit. The BHDM6 has the fish hole.

Carbide tipped, so it handles masonry as well as wood. That is the point of the carbide on the BHDM6: electricians and alarm installers drilling from inside a building out through a brick or block exterior wall hit mortar, old nails, and sometimes rebar wire, and a high speed steel bit gives up. For a straight wood-only run a plain auger is cheaper, but it will not survive the masonry.

A 5/16 inch bore suits the usual low voltage work this bit is bought for: alarm and security cable, thermostat wire, coax, Cat5e/Cat6 single runs, and small pull strings. If you are pulling NM-B branch circuit cable or multiple jacketed runs, step up to a larger diameter bell hanger bit instead. The BHDM6 is the 5/16 inch size.

One bit per pack, supplied in a pouch. If you are stocking a van or a service truck and want spares on hand, order the quantity you need up front, since each unit is a single piece rather than an assortment.