Long Wood Drill Bits: Check Working Length Before You Buy

For a deep hole through solid timber, start with a long auger bit. For accurately positioned woodworking holes, consider an extra-long brad-point bit. A long spade bit is an option for service holes in clean wood, while a flexible installer bit serves in-wall cable work—not precision joinery.

The buying trap is length: overall length is not the same as working length. Decide whether you need to drill through more wood or simply reach wood farther away from the chuck.

Choose the cutting design first

Your task	Bit to consider	What matters most
Deep holes in beams, posts or thick timber	Long auger	Working length, chip removal and self-feeding tip
Accurately located holes in a woodworking project	Extra-long brad point	Centring point, cutting spurs and an aligned setup
Service holes through clean framing or stacked wood	Long spade	Required reach, exit finish and clean-wood rating
Drilling framing inside a wall cavity for cable routing	Flexible installer auger	Safe positioning, shaft reach and compatible placement tools

Auger: Its screw tip pulls the bit into the wood, rather than relying entirely on your pushing force. Bosch describes its PRO Wood auger as intended for deep holes in hardwood and softwood, with a flute designed to remove chips. That makes this design a sensible starting point for deep timber boring; the self-feeding action also means you must be ready to control the drill. Bosch auger specifications.

Brad point: The centre point locates the start, while sharp outer spurs reduce splintering. Bosch’s PRO Wood range includes long versions with two chip-removing flutes. Choose this design when hole placement and finish matter, but do not expect a centred start to guarantee a straight deep hole without careful alignment. Bosch brad-point specifications.

Spade: A long paddle-style bit is worth considering when you need reach for a service hole rather than a fitted woodworking joint. For example, Diablo’s DSP3020 is a 1/2-inch-diameter, 16-inch-long spade bit with a 1/4-inch hex shank, listed for clean hardwood, softwood and plywood. Do not assume that every spade bit is suitable for embedded nails. Diablo DSP3020 specifications.

For the broader differences between cutting designs, see our guide to drill-bit types and uses.

Separate drilling depth from reach

Check these dimensions before ordering:

• Cutting diameter: The nominal hole size.
• Working length: The manufacturer’s stated working portion; use this rather than overall length when assessing a deep solid-wood hole. It is not a guarantee of achievable depth in every setup.
• Overall length: Tip to shank end, including the portion held in the chuck.
• Shank size and shape: What must fit your drill or holder.

Two examples show why the distinction matters:

Exact bit	Overall length	Listed working length	Shank
Diablo DAG3030, 1/2-inch auger	17-1/2 in.	13-1/2 in.	5/16-in. hex
Bosch 2608577722, 8 mm brad point	250 mm	190 mm	8 mm cylindrical

These are manufacturer-listed dimensions, not measured drilling results. Sources: Diablo DAG3030 and Bosch PRO Wood brad-point range.

Do not plan a 17-1/2-inch-deep solid-timber hole solely because the auger is 17-1/2 inches long: its listed working length is only 13-1/2 inches. For a blind hole, also distinguish the depth reached by the projecting brad or screw point from the depth of the full-diameter hole.

An extension can move the cutter farther from the drill, but it does not add flute length. Verify bit retention, shank compatibility and whether the coupling must pass through the hole. Coupling size can differ from shank size: Klein’s 53723 flex-bit extension has a 3/16-inch shank but a 7/16-inch connection diameter. Buy an extension specified for your drilling bit, not merely a holder that accepts the shank.

Check drill fit and hidden obstacles

A hex shank is not necessarily 1/4 inch. The Diablo auger above has a 5/16-inch hex shank, so it will not fit a standard 1/4-inch hex holder directly. Check the exact shank and your chuck capacity; also check the drill’s wood-boring limits for the bit type and diameter.

Where nails are plausible, select an explicitly nail-embedded-wood-rated bit. Diablo lists the DAG3030 for that application, unlike the clean-wood DSP3020. That rating is not permission to drill through unknown obstructions.

A flexible bit’s length is principally about access. Klein’s 53718 is a 9/16-inch by 54-inch flex auger intended to drill wood within a wall, with holes for pulling wire and compatibility with a placement tool. Its 54-inch overall length is not a solid-timber drilling-depth rating. Establish the drilling path and hidden services before starting; Klein warns never to use it on or near live electrical circuits. Klein 53718 specifications and warnings.

Drill without forcing the long shaft

Clamp the work securely and wear eye protection. Start at low speed with the tip touching the wood, stay below the bit’s maximum speed rating, and apply pressure directly along its axis—not sideways. Bosch’s long-bit safety instructions warn that a freely rotating long bit can bend, and excessive pressure can cause breakage or loss of control. If the bit binds, switch off immediately rather than forcing it; be prepared for kickback. Bosch drill safety instructions.

Follow the bit maker’s chip-clearing instructions. Bosch’s wood-drilling guidance specifically warns that twist bits can overheat unless withdrawn frequently to clear their flutes. Use a backing block where accessible to reduce exit splintering, and ease the feed as the cutter approaches breakthrough. Bosch wood-drilling guidance.

Choose the shortest bit that meets both the working-depth and access requirements. Extra length should solve a specific clearance problem, not substitute for the right cutter or a controlled setup.