Bosch Expert SelfCut Speed spade bit in 40mm diameter, 152mm long. Self-feeding tip pulls the bit into the wood for fast, clean holes with less effort. Fits standard 1/4 inch hex chuck. Suitable for electricians, carpenters, and installers.
Wood spade bits have been around forever, but not all of them are made equal. The Bosch Expert SelfCut Speed Spade Bit is one of the better-designed options on the market, and the 40mm x 152mm size is a particularly useful one for anyone drilling cable or pipe runs through timber frames, joists, or stud walls. It is built for professionals who are drilling multiple holes in a day and cannot afford to waste time clearing chips or fighting the drill through dense hardwood.
The standout feature is Bosch’s self-feeding thread tip. Rather than requiring you to push the bit into the material, the thread grabs and pulls itself forward once it bites. That means less pressure needed on the drill, less fatigue over a long run of holes, and generally better control. On a ladder or in an awkward roof space, that matters more than you might think.
What Makes These Wood Spade Bits Worth Using
The wave-shaped cutting edges are the other part of the equation. Conventional flat spade bits can pack up with chips, especially in softwood or when drilling at speed. The wave profile on the SelfCut creates a more aggressive chip ejection action, keeping the flutes clearer and the bit running cooler. You will notice the difference most on through-holes in thicker timber where a standard bit would have you withdrawing every inch to clear the waste.
At 152mm total length, this bit reaches comfortably through a standard stud wall or floor joist without needing an extension. The 1/4 inch hex shank fits any standard hex-chuck drill driver or three-jaw chuck, so there is no fussing about with adaptors on site. That shank size also means it drops straight into a quick-change chuck, which is worth its weight when you are swapping between bit sizes repeatedly.
40mm: The Right Size for Cable and Conduit Work
The 40mm diameter sits in a sweet spot for electrical and plumbing first fix. It is wide enough to take a standard conduit or a bundle of cables comfortably, but not so large that it starts to seriously weaken the timber. Electricians running cable through timber frames will find themselves reaching for this size regularly. The Expert range from Bosch is their trade-grade line, so the steel quality and edge retention are noticeably better than budget spade bits that go blunt after a handful of holes.
Pro Tip: When drilling through multiple joists in a row, keep the bit spinning as you withdraw it from each hole rather than stopping dead, as this clears any remaining chips and keeps the edges sharper for longer.
This spade bit is used wherever clean, fast holes need to go through timber. First fix electrical work is the obvious application, drilling through joists and studwork for cable runs, but it is equally at home in carpentry for pipe chases, plumbing rough-in work, and general construction carpentry. It handles softwood and hardwood, engineered timber, and structural carcassing without complaint. Roofers, joiners, and ground workers running services through floor structures will all find the 40mm diameter a regular go-to size on site.
Best For
First fix electrical cable runs
Plumbing pipe chases through timber
Stud wall and joist drilling
Carpentry and joinery work
General construction drilling in wood
Compatible With
1/4 inch hex shank drill drivers
Three-jaw chuck drills
Quick-change hex chuck systems
Standard corded and cordless drills
Key Specifications
Diameter: 40mm
Total length: 152mm
Shank: 1/4 inch hex
Self-feeding threaded tip
Wave-shaped cutting edges
Bosch Expert series steel
Not suitable for: Not suitable for drilling into masonry, metal, or composite materials. Not designed for use with impact drivers where the hex shank may be subjected to rotational hammering rather than pure rotation.
Mark your hole position clearly before you start, especially on joists where accuracy matters for structural reasons. Let the self-feeding tip do the work once it bites: apply light, steady forward pressure and allow the thread to pull the bit through rather than forcing it. There is a temptation to lean in hard, but that usually just causes the bit to wander at entry.
On thicker sections of timber, withdraw the bit briefly mid-hole to clear chips if you notice the drill straining or slowing significantly. Keep the drill speed moderate rather than flat out, especially when breaking through the far face, where a sudden exit can split the surface timber if you are running at full speed.
Mark the hole centre clearly with a pencil or awl before drilling
Select a suitable drill or driver with a 1/4 inch hex chuck or standard three-jaw chuck
Position the self-feeding tip on the mark and apply light forward pressure to start the thread
Allow the bit to pull itself into the timber once the tip has engaged
Maintain steady drill speed without forcing additional pressure through the drill
Withdraw briefly on deep cuts to clear chips if the drill begins to labour
Ease off the feed rate as the bit approaches breakthrough on the far face to avoid splitting
Will this spade bit fit a standard cordless drill driver?
Yes. The 1/4 inch hex shank fits any drill driver with a hex chuck or quick-change chuck, and it will also fit a standard three-jaw chuck without any adaptor. Most cordless drills and drill drivers on site will take it without issue.
Is the 40mm SelfCut bit suitable for drilling through engineered timber joists like I-beams?
It will drill through the timber flanges of I-joists, but always check with the joist manufacturer's guidelines before drilling through engineered structural members. Position and hole size restrictions apply to I-joists, and drilling in the wrong zone can affect structural performance regardless of what bit you use.
The Bosch Expert SelfCut Speed Spade Bit is manufactured from high-grade steel with precision-ground cutting edges. The self-feeding screw tip is machined to a consistent thread pitch that initiates pull-through reliably across timber densities. The wave profile on the main cutting wings increases chip clearance compared to a flat-ground spade, reducing heat build-up and extending edge life over repeated use. This bit is part of Bosch's Expert line, which is positioned above the Standard range in terms of material quality and cutting geometry.
Diameter
40mm
Total Length
152mm
Shank Type
1/4 inch hex
Shank Diameter
6.35mm (1/4 inch)
Tip Type
Self-feeding threaded tip
Series
Bosch Expert
Material
High-grade steel
Quantity
1
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