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Reduced Shank Drill Bits

Reduced Shank Drill Bits

Reduced Shank Drill Bits

Reduced Shank Drill Bits (also known as Silver and Deming Drill Bit, Reduced Shank Twist Drill or Silver Deming Bit) are twist drills with a drilling diameter larger than the shank, so a hole bigger than 13mm can be drilled from a standard 13mm chuck. BNA stocks 31+ of these ex stock from our Brisbane warehouse, covering the full range of diameters, lengths and shank styles that engineers, tradies, manufacturers and DIY users need for everyday drilling tasks. Same-day dispatch on online orders placed before 1pm.

Also known as: Silver and Deming Drill Bit, Reduced Shank Twist Drill, Silver Deming Bit.

Drill Bit Construction & Materials

Alpha Gold Series HSS M2 high-speed steel with a Gold Series surface treatment that adds wear resistance to the cutting flutes. The standard for general steel, alloy and timber drilling in oversize holes.

Alpha HSS Black Oxide Standard M2 HSS with a black oxide surface finish. The oxide layer reduces chip welding (galling) on the cutting edge in steel and reduces glare on the workpiece. Holds up well in plain steel.

Drive & Use

Reduced shank is a workshop convenience for occasional oversize work. The drill that drives them is whatever 13mm-chuck drill you already own — bench drill, cordless, drill press.

Because the shank is undersized relative to the cutting edge, the bit flexes more under load than a same-diameter full-shank bit would. Run slower, use firmer steady pressure, and keep the chuck tight.

Pilot hole is mandatory. Drill a 6mm-8mm pilot before any reduced-shank cut. The pilot prevents the bit from walking and reduces the cutting load on the oversized head.

Cutting fluid is essential. The bigger cutting head generates more heat than a same-shank twist drill would, and the longer time at temperature dulls the edge faster. Steel needs fluid; aluminium can run dry; stainless absolutely needs fluid.

Sizing & Measurements

Diameter range 13mm to 18.5mm cutting diameter in 0.5mm steps. The shank is 13mm regardless of cutting diameter.

Length range Overall length 130mm-180mm typical. Flute length is shorter than a jobber of the same cutting diameter would be, because the shank takes up part of the overall length.

Shank 13mm round shank, period. This is the whole point of the reduced-shank format: oversize holes from a standard 13mm chuck without upgrading the drill.

Steps every 0.5mm from 13mm through 18.5mm. For larger holes (19mm and up), use a step drill, holesaw or appropriate dedicated bit — reduced shank stops at 18.5mm in this range.

For bolt clearance through plate, drill bolt diameter plus 0.5mm-1mm. M16 = 16.5mm-17mm reduced-shank bit.

If you only need one oversize hole and have a workshop drill press, a single bit costs much less than upgrading a 13mm chuck to a 16mm or 20mm chuck.

WHY AUSTRALIA TRUSTS BOLT & NUT

With 15+ years selling fasteners and drilling tools online from Brisbane, we hold over 25,000 stock lines and 200 million pieces. 98.75% of online orders placed before 1pm leave same day. Save more as you buy more — we offer up to 13 price breaks plus 3 spend-tier discounts. Read our customer reviews or get in touch if you need help picking the right drill bit, holesaw or set for the job.

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