Mower Blade Center Hole Types Explained
2026-11-10 · 7 min read
A mower blade centre hole comes in four main types — round, star (5, 6 or 7 point), keyed or slotted, and multi-bolt — and the shape, not the diameter, decides whether the blade mounts on your spindle. Match the centre-hole pattern first, because every other measurement is useless if the blade will not seat.
Why does the centre hole decide the fit?
The centre hole decides the fit because it is what locks the blade to the spindle at a fixed angle and height. A blade with the right length, width and thickness still will not mount if the hole pattern is wrong, and the mismatch is not obvious until someone tries to fit it. The hole is the gate; the other numbers are the detail.
Most decks use one of four patterns, so identifying the shape is the first step before any order. Our blade measuring guide shows how to record the hole, and the model index lists the centre-hole type for every profile we cut.
What are the round centre hole blades?
Round centre hole blades use a plain circular bore, often with a fixed diameter such as 11/16" or 3/4", and they seat on a matching round spindle shaft. This is the simplest pattern and the easiest to measure, because only the bore diameter and the retaining washer matter. Round holes suit many walk-behind and lighter rider decks.
| Centre hole type | Common on | Fails if |
|---|---|---|
| Round | Walk-behind, light riders | Bore diameter mismatched |
| 5/6/7-point star | Garden tractors, zero-turn | Point count wrong |
| Keyed / slotted | Fixed-angle decks | Keyway not aligned |
| Multi-bolt | Some commercial decks | Bolt circle off |
These four patterns cover the vast majority of North American decks, so naming the shape is usually enough to rule a blade in or out. The 742-0616 mulching blade and the 942-04308 high-lift blade show two of the patterns we hold in stock.
What are star centre hole blades?
Star centre hole blades carry a 5, 6 or 7 point star that locates on a matching star spindle, and the point count must match exactly or the blade will not seat. A 7-point blade will not mount on a 6-point spindle, even though both look "star shaped" at a glance. The point count, not the overall size, is what matters.
This is the pattern most garden tractors and zero-turn decks use, so it is the one to check carefully. Counting the points before ordering avoids the most common fit failure we see, where length and width were right but the star did not match. A 110-6837-03 mulching blade is one of the star-pattern profiles in our range.
What are keyed and multi-bolt centre holes?
Keyed and multi-bolt centre holes locate the blade at a fixed angle rather than relying on a star or plain round bore. A keyed hole has a slot or flat that lines up with a key on the spindle, while a multi-bolt pattern uses two or more bolts through the blade into the spindle adapter. Both fix the blade's rotational position precisely.
These patterns appear on decks where the blade angle must stay exact, and they are less forgiving of a wrong adapter. When the hole is keyed or bolted, the adapter that sits between blade and spindle must match too. Tell us the machine model and we will map it to the correct centre-hole profile.
How do you measure a centre hole correctly?
Measure a centre hole by noting the shape first and the diameter second, because the shape is what decides the mount. For a round hole, measure the bore; for a star, count the points; for a keyed hole, note the keyway; for a bolt pattern, measure the bolt circle. The diameter alone will mislead you.
Take a close photo of the hole from straight above, next to a ruler, so the shape is unmistakable. Our measuring guide lists the full set of facts to send, and the model index shows the centre-hole type each of our blades uses.
What steel and hardness should a centre-hole blade use?
A centre-hole blade should be cut from 40Mn manganese steel and hardened to a 45–50 HRC band, which holds the edge through grit yet resists cracking on hidden stone. The hole pattern is about fit; the steel and heat-treat are about how long the blade lasts under load.
We run production in Guangde, Anhui, where the plant has made blades since 2008 and now employs more than 800 people with a daily capacity of 50,000 pieces. The same heat-treat control is detailed on our quality page, which is the part of production that most affects working life.
Frequently Asked Questions
Can a round-hole blade fit a star spindle?
A round-hole blade cannot fit a star spindle, because the shapes are not interchangeable — the star points must locate in matching slots. Forcing a round blade onto a star spindle leaves it loose and unsafe. Always match the hole shape to the spindle pattern.
Does bore diameter matter on a round hole?
Bore diameter matters on a round hole, because a blade with the wrong bore will not sit on the shaft or will rattle under load. Measure the bore — common sizes are 11/16" and 3/4" — and match it to your spindle before ordering.
How do I count star points correctly?
Count star points by looking straight down at the hole and tallying the outward points, because 5, 6 and 7 point stars look similar at a glance. A 7-point blade will not seat on a 6-point spindle, so the exact count decides the order.
Are your centre-hole blades original equipment parts?
We are an independent manufacturer and not an authorised dealer, so our blades are not original factory parts. They are made to match the original specifications of the part number you send, cut from 40Mn steel and held in the 45–50 HRC band.
What is the minimum order for custom centre-hole blades?
The minimum order is 300 pieces per profile, which covers the setup and heat-treat run for a made-to-sample blade. Send the old blade or its number and we will confirm the centre-hole pattern, profile and run size before cutting.
More on this: How Mower Blades Are Made: From Steel to Sharp Edge · 10B38 Boron Steel vs 40Mn Mower Blades
Blade part numbers linked to this article
The model pages below carry the deck size, centre hole, thickness and replacement numbers for the blades discussed above.