Technical Guides
How to get more out of the tools you buy
26 working guides — speed charts, size charts, failure diagnosis, selection and storage. Written by the people who spec and inspect these tools: no filler, just what changes the result on the job.
- Drill size chartAll four sizing systems + converter
- mm ↔ inch conversionEvery 64th and every 0.1 mm
- Number & letter gauges#1–#80 and A–Z in mm
- Metric tap drillsM2–M24, coarse and fine
- UNC / UNF tap drillsImperial threads + NPT
- Clearance holesM1.6–M24 through holes
- Wall plug sizesYellow, red, brown, blue
- Pilot holes for screwsGauge and metric, both woods
- Drill speed / RPMBy material and diameter
- Hole saw sizesLocks, pipes, downlights
- Grinder disc sizes100–230 mm and max RPM
- Grinding wheel typesType 27, 41 and 42
- Flap disc grits40 / 60 / 80 / 120 compared
- What is in a drill set13, 19, 25 and 115 piece
Depressed Center Grinding Wheels: Type 27, 41 and 42 Explained
The number stamped on a bonded disc describes its shape, and the shape decides whether it grinds or cuts. Type 27, 41 and 42 compared, the full size and thickness chart, and why a cutting disc used flat is the most common way one comes apart.
Read the guideHow-To & Technique
09 guidesSpeeds, feeds and the habits that make tools last.
Pilot Hole Size Chart for Wood Screws: Gauge, Metric and the Clamp Trick
Split boards and snapped screws both come from the same missing hole. Pilot and clearance sizes for #4–#14 and 3–6 mm screws, the root-diameter rule behind the chart, and the two-hole trick that pulls joints tight.
UNC & UNF Tap Drill Chart: Imperial Threads with Metric Drill Equivalents
Imperial machines did not retire; they got exported. Tap drill sizes for UNC, UNF and NPT threads — with the nearest metric bit for every one, and the one-line rule that generates the whole chart.
Wall Plug Drill Size Chart: Yellow, Red, Brown, Blue — and Why Plugs Spin
Yellow takes a 5 mm bit, red a 6, brown a 7, blue a 10 — and a worn masonry bit ruins all four. The full plug-to-drill-to-screw chart, hole depth rules, and which walls must never see hammer mode.
Drilling Into Concrete: Masonry Bits, Hammer Mode and SDS-Plus Explained
Concrete is not drilled so much as pulverised — which is why an ordinary drill stalls in it and an SDS-Plus walks through. The three tool classes, the carbide tip that does the work, anchor hole sizes, and what to do when you hit rebar.
How to Drill Stainless Steel Without Work-Hardening the Hole
Stainless punishes hesitation: let the bit rub for two seconds and the hole grows a glaze harder than the bit itself. The RPM numbers, the feed rule, and how to rescue a hole that has already hardened.
Step Drill Bits: How to Use Them Properly in Sheet Metal
A twist drill in thin sheet grabs, triangulates the hole and spins the workpiece. A step drill cannot — if you run it at half the speed you think it wants. How the cone works, the RPM table, and where its limits genuinely are.
Metric Tap Drill Size Chart: M2 to M24, and the Rule Behind It
The drill size for any metric tap is one subtraction away — but the chart is faster. Coarse and fine pitch from M2 to M24, clearance holes, and the thread-engagement rule that stops taps snapping in the hole.
Why Drill Bits Keep Breaking — and the Five Fixes That Actually Work
Snapped bits, burnt tips, holes that wander off centre. Each failure leaves a signature that tells you exactly what went wrong. Here is how to read it and what to change.
Drill Bit Speed Chart: The Right RPM for Steel, Stainless, Aluminium and Wood
Running a drill too fast is the single most common reason bits die early. Here is the RPM to use for each material and diameter, the formula behind it, and how to tell from the chips whether you got it right.
Selection Guides
13 guidesWhich specification for which job — with the charts.
Drill Bit Conversion Chart: mm to Inches, Fractions, and Which Bit to Actually Use
Every stock metric bit from 1 to 13 mm as a decimal inch and nearest fraction, every 64th from 1/64" to 1" in millimetres, and the substitution rule that says when 0.1 mm matters and when it is noise.
HSS-R, HSS-G, HSS-E and HSS-Co: What the Codes on a Drill Bit Mean
HSS-G and HSS-Co describe how the bit was made and what it is alloyed with. TiN describes a coating three microns thick. Confusing the two is why buyers pay for a gold bit that dulls faster than a plain one.
Clearance Hole Chart for Metric Screws: M2 to M24 Through-Hole Sizes
The hole the bolt passes through, not the one it threads into. ISO 273 close, medium and free-fit sizes for M1.6 to M24, counterbore dimensions for socket screws, and why a joint that will not pull tight is almost always a missing clearance hole.
Number and Letter Drill Bit Sizes: The Full #1–#80 and A–Z Chart in mm
A drawing calls for a #11 drill and the rack only speaks millimetres. Every number gauge from #1 to #80 and every letter from A to Z, converted to mm and decimal inch, with the metric bit that actually substitutes for each one.
Angle Grinder Disc Sizes: 100 to 230 mm, Max RPM, and What Fits What
Disc diameter sets the machine, the arbor and the maximum RPM — it is a safety system, not a preference. The 100–230 mm size chart, the 80 m/s rule behind the printed limits, and the job-to-disc table.
Hole Saw Size Chart: Locksets, Pipe Runs, Downlights — and the Right RPM
A door lockset is 54 mm, a sink tap 35, a pipe hole is the OD plus clearance. The job-to-size chart, bi-metal vs TCT vs diamond, and the low RPM figures that keep teeth on the saw.
Wood Drill Bit Types: Brad Point, Spade, Auger or Hole Saw — Which and When
Five bit families drill wood, and each is unbeatable at exactly one thing. The comparison table — size range, hole quality, speed, depth — plus the RPM figures and the blowout trick.
Diamond Blade Types: Segmented, Turbo or Continuous Rim — Which Cuts What
A diamond blade does not cut — it grinds, and the rim shape decides everything: cut speed, edge chipping, what material it survives. The three rim types, the wet/dry rules, and why a "blunt" blade usually is not dead.
Drill Bit Size Chart: mm to Inch, Fractional, Number and Letter Sizes
Four sizing systems are alive in the same market: metric, fractional inch, number and letter gauges. Type any size into the converter and get the other three — plus the full tables, the clearance holes, and how to measure a bit whose markings wore off.
Flap Disc Grit Guide: What 40, 60, 80 and 120 Are Each For
Grit 40 removes a weld, grit 120 makes stainless look finished — and using either where the other belongs wastes discs and workpieces. A working grit chart, zirconia vs aluminium oxide, and the T27/T29 angle rule.
Phillips vs Pozidriv: Telling PH and PZ Apart Before They Chew a Screw
Half the "worn out" bits in any workshop are the wrong system in the wrong screw. The four tick marks that identify Pozidriv, why a PH2 strips a PZ2 recess, and which sizes actually move.
HSS, Cobalt or Carbide: Which Drill Bit for Which Job
HSS 4241, M2, M35, M42, TiN-coated, solid carbide — six grades, real differences, and the honest answer to which one is worth the money for each material.
TCT Saw Blade Tooth Count: Picking the Right Blade for Each Material
Tooth count, grind type and hook angle decide whether a blade rips fast, cuts glass-smooth, or destroys the panel. Here is what each number on the blade actually means.
Maintenance & Safety
02 guidesChecks and storage that prevent failures.
Storing Cutting Tools: Stopping Rust, Chipping and Silent Shelf-Life Losses
Tools that never got used can still be ruined by the warehouse. Humidity, stacking and shelf life quietly write off stock — here is how to prevent each one.
Cut-Off Wheel Safety: The Checks That Stop a Disc Coming Apart
A 115 mm disc at 13,000 RPM has its rim moving at 80 metres per second. When one bursts, the pieces do not stop for anything. Four checks — taking under a minute — prevent almost every failure.
Sourcing & Import
01 guideBuying tools in volume, without the surprises.
Need a spec recommendation for a specific job?
Tell us the material, the machine and the volume. We'll tell you which grade actually suits it — and quote it within 24 hours.