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Riving knife too thick for the saw blade: 8 mm rule

Updated: 22 October 2026

The knife stops at the mouth of the kerf and will not enter. A riving knife too thick for the saw blade is thicker than the slot the teeth cut, or no longer thicker than the plate. It must be thicker than the plate and thinner than the kerf, within 8 mm at table level, and no more than 25 mm below the top of a blade under 600 mm. Fitting steps are on the [how to change a table saw blade](/hub/saw-accessories/254mm-x-30mm-circular-saw-blade/sub/254mm-x-30mm-circular-saw-blade-how-to-change) page. Figures are from amazon.co.uk on 20 October 2026 and from HSE guidance. A link may earn a commission. The eight listings are in the [254 mm x 30 mm circular saw blade comparison](/hub/saw-accessories/254mm-x-30mm-circular-saw-blade).

The knife stops at the mouth of the kerf and will not enter. A riving knife too thick for the saw blade is thicker than the slot the teeth cut, or no longer thicker than the plate.

Our top picks

BGS Do it yourself BGS 3954 40-tooth blade

Best overall

BGS Do it yourself BGS 3954 40-tooth blade
6.2/10about £10.52
View offer
Saxton Blades Saxton TCT25480T 80-tooth blade

Alternative

Saxton Blades Saxton TCT25480T 80-tooth blade
7.9/10about £19.99
View offer
Starrett Starrett CCS254-60DW 60-tooth blade

Alternative

Starrett Starrett CCS254-60DW 60-tooth blade
5.2/10about £19.99
View offer
On this page
  1. 1.Thicker than the plate, thinner than the kerf
  2. 2.8 mm at the table, 25 mm at the top
  3. 3.A 2.0 mm splitter against this set
  4. 4.When the listing does not let you check

Thicker than the plate, thinner than the kerf

Kickback is why the knife exists. On a rip, the kerf can close behind the teeth and throw the board back. HSE says the knife sits within 8 mm of the blade, thicker than the plate and thinner than the kerf. WIS16 draws the same inequality. One printed number cannot prove it. A seller's average of kerf and plate is not that rule. The knife has to sit strictly between the two thicknesses. A 254 mm blade is under 600 mm, so the height limit applies to every blade here. If the knife cannot be changed, choose the blade to suit it.

8 mm at the table, 25 mm at the top

L114 says the gap at table level is not over 8 mm, and, for a blade under 600 mm, the top of the knife is no more than 25 mm below the top of the blade. POS01 repeats both figures. Measure the 8 mm where the timber runs, not at the rim by the guard. Einhell's TC-TS 254 U asks for 3 mm to 8 mm and prints a 2.0 mm splitter beside a supplied blade of 254 x 30 x 2.4 mm. That pair is Einhell's own blade, not a test of these listings. Check the 25 mm at the height you will actually rip. Raising the blade and leaving the knife low breaks the limit without a blade change.
BGS Do it yourself BGS 3954 40-tooth blade

Testsieger

BGS Do it yourself BGS 3954 40-tooth blade
6.2/10about £10.52
View offer

A 2.0 mm splitter against this set

Saxton TCT25480T is the only kept card that prints both sides: plate 1.8 mm and kerf 2.6 mm. A 2.0 mm Einhell splitter sits between those figures. The 40-tooth and 60-tooth Saxton cards print a 2.6 mm kerf and no plate. Saxton's own page adds 1.8 mm on the 60-tooth blade. Say that as a second source, and do not write it into the blank amazon field. Trend prints a 2.4 mm kerf and no plate. Trend's own page prints 1.6 mm, which the amazon file alone cannot show. BGS 3954 prints 3.2 mm in the title and 1.8 mm and 2.8 mm in the bullets. Do not pick among them to make a 2.0 mm knife look as if it fits. Axminster's AP254TS wants a 2.5 mm knife and a maximum blade of 250 mm, so a 254 mm blade is already too large.

When the listing does not let you check

Starrett calls 2 mm both thickness and kerf, so the knife cannot be thicker than the plate and thinner than the kerf at the same time. The 30 mm thickness field is the bore. METAK prints no kerf and no plate. A UK review's 1.8 mm figure is a zero-clearance insert, not a listed kerf. BATIOPV prints 1.8 mm and 2.2 mm without saying which is the plate. If the knife will not enter, the kerf is too narrow or something is bent. Do not force it. On work equipment, stop if the knife, the brake or the extraction is missing. Do not sweep wood dust. Use at least a Class M vacuum. Hardwood dust can cause nasal cancer. A change that leaves the knife in the drawer is not finished.

Common questions

Why will the knife not enter the kerf?
The knife has to be thinner than the kerf. If it is 2.0 mm and the true kerf is under 2.0 mm, it will not enter. BGS 3954 prints 3.2 mm in the title and 1.8 mm and 2.8 mm in the bullets. Do not file the knife to suit a number you are not sure of.
How high should the top of the knife be?
For a blade under 600 mm, L114 says the top of the knife is no more than 25 mm below the top of the blade. Check it at the height you will actually rip. A knife that is thick enough and too low still leaves the top of the cut unsupported.
Does a 2.0 mm Einhell splitter fit a plate of 1.8 mm and a kerf of 2.6 mm?
On the printed figures, yes. 1.8 mm is under 2.0 mm, and 2.0 mm is under 2.6 mm, which is the HSE inequality. Saxton TCT25480T is the amazon card here that prints that pair. The saw still has to accept a 254 mm blade. The 8 mm gap and the 25 mm height are checks you make on the machine.
What if thickness and kerf are both printed as 2 mm?
Then the inequality cannot be true. The knife would have to be thicker than 2 mm and thinner than 2 mm at the same time. That is what the Starrett bullet does. The 30 mm thickness field on the same listing is the bore, not a rescue. Treat that card as a cross-cut blade with rings, not as a knife match.
Is a seller's (kerf + plate) / 2 the same as the HSE rule?
No. Some sellers suggest the knife thickness as the average of kerf and plate. HSE requires the knife to be greater than the plate and less than the kerf. An average is not what L114 says. Use the inequality, then the 8 mm at the table and the 25 mm at the top.

Related pages

254 mm x 30 mm circular saw blade buying guide

254 mm x 30 mm circular saw blade

Best 254 mm circular saw blade: rip, sheet or mixed

How to change a table saw blade: unplug, then refit

24 tooth or 80 tooth circular saw blade for your cut

Sources

Public UK sources from the research digest, used for this page in October 2026. Prices, stars and review counts are from the eight amazon.co.uk listings captured on 20 October 2026. HSE knife and wood-dust guidance applies where the saw is work equipment. It is not a certificate for a domestic blade. No listing here is a laboratory test.

  1. HSE, Circular saw benches (retrieved 20 October 2026)
  2. HSE WIS16, Circular saw benches (retrieved 20 October 2026)
  3. HSE L114, Safe use of woodworking machinery (retrieved 20 October 2026)
  4. HSE, Wood dust (retrieved 20 October 2026)
  5. HSE WD3, Hardwood dust (retrieved 20 October 2026)
  6. BSI, BS EN 847-1:2017 (retrieved 20 October 2026)
  7. Einhell TC-TS 254 U manual (retrieved 20 October 2026)
  8. Axminster AP254TS manual (retrieved 20 October 2026)