What do all the numbers on a circular saw blade mean?

A circular saw blade carries six or seven printed numbers and most people read only the first. The result is a shelf of blades that all cut adequately and none cut well. Once you know which figures are constraints and which are choices, blade selection takes seconds.

Safety

Step by step

1. Read the diameter — a constraint.Printed largest, in millimetres. It must be the size your saw is designed for. A smaller blade reduces the depth of cut and may not reach past the guard properly; a larger one will not fit under it at all.
2. Read the bore — a constraint.The centre hole diameter, which must match the saw's arbor. Common sizes differ between brands. Reducing rings supplied with a blade are for one specific step down and must seat fully; anything improvised is dangerous because the blade will run out of true.
3. Read the maximum rpm — a constraint.It must be equal to or greater than the saw's no-load speed, which is on the saw's rating plate. This matters most with large-diameter blades and with blades bought for a different machine.
4. Read the kerf — mostly informational.The width of the slot the blade cuts, set by how far the carbide tips project beyond the plate. A thin-kerf blade removes less material, so it needs less power and suits a cordless saw; it also flexes more. The kerf must be wider than the riving knife is thick, or the knife jams in the cut.
5. Read the tooth count — the main choice.Fewer teeth cut faster and rougher and clear waste better. More teeth cut slower and cleaner and generate more heat. On a 165–190mm cordless saw, roughly 16–24 teeth for ripping and construction, 40–48 for clean crosscuts and sheet material, 60 or more for laminate and fine work.
6. Read the tooth grind — the other main choice.ATB (alternate top bevel) teeth are bevelled left and right alternately and slice fibres cleanly, which is the general choice for timber and sheet. FTG (flat top grind) teeth are square-topped and chisel the fibres apart, which is fast along the grain. TCG (triple chip grind) alternates a chamfered tooth with a flat one and is the choice for laminate, melamine, solid surface, plastics and aluminium.
7. Note the rake or hook angle where it is stated.Positive hook means the teeth lean forward into the cut — aggressive and fast, right for a hand-held saw ripping timber. Negative hook means they lean back — much less grabby, which is why mitre saw blades and blades for laminate and non-ferrous metal are ground that way.
8. Check the direction arrow and the expansion slots.The arrow on the blade must point the same way as the arrow on the guard. The curved slots cut into the plate are expansion slots, letting the steel grow as it heats without buckling; they are not damage.

Tips

• Two blades cover almost all home use: a 24-tooth for breaking down construction timber and a 48-tooth for clean cuts in sheet. Buy the good version of each rather than a set of six cheap ones.
• A blade covered in dark resin cuts like a blunt blade. Clean it before you conclude it needs replacing.
• Blade quality shows in the plate as much as the teeth. A cheap blade with a thin, poorly tensioned plate wobbles under load and cuts a wider, rougher kerf than its specification suggests.

Common mistakes

• Fitting a high tooth count blade to rip thick timber — There is nowhere for the waste to go, the blade overheats, the timber burns and the motor labours. Deep cuts need big gullets and few teeth.
• Using an adaptor to fit a blade with the wrong bore — Any eccentricity is multiplied by the rim speed. The blade runs out of true, cuts a wide ragged kerf and stresses the arbor.
• Ignoring the maximum rpm on a blade bought second-hand — Large blades intended for slow machines can burst if spun at hand-held saw speeds.

Questions people ask