are lawn mower blades universal

A new blade can make a huge difference to the performance of your mower and the quality of cut. I like to change my blade every three years. But the correct blade is critically important, a mower blade tip travels at more than 200 mph. I never take a chance with a poor fitting or damaged blade.

So, are lawn mower blades universal? No, lawn mower blades are not universal, they are mower specific. A mower blade must be a exact fit and torqued to manufacturers specification.

I’m a mechanic for more than twenty years and in this post I’ll share how to identify the correct blade for your mower. I’ll also cover costly and dangerous mistakes to avoid when choosing and fitting a mower blade.

Lawn mower blade torque

Torque blade to spec

How to identify your blade

Identifying your blade is obviously the first important step. Getting this wrong can lead to an ill fitting and dangerous blade. Luckly, Identifying your blade is pretty easy, there’s a few ways to go about this.

Mower make and model

The first way is to identify your mower by the model and make, you’ll usually find the badge or label on the mower chassis or deck. I know for some, the label will be missing or unreadable, but not to worry, we have other ways to id the blade.

If you do have a label, inputting make and model number in Amazon will likely give you a list of suitable blades. I like to use genuine parts if possible, the fit and quality is usually best.

A good seller will list the part number also, which brings us to the second way to identify the correct blade.

Lawn mower model label

Make and model number label

blade part numbers

Every mower blade will have a part number stamped into the metal. The numbers are unique to that part and very often just typing said number in google will offer a list of sellers.

However I know blade part numbers can be difficult to spot, what with years of grass clippings and corrosion etc.

Lawn mower blade part number

blade part numbers

blade sizing

The third way to id the blade is by sizing. I’ll often have no choice but size a blade, as customers will just walk in with blade in hand and no other details.

There’s no mystery to sizing a mower blade correctly, however just before we do we, need to identify the type of blade.

There are two common types of lawn mower blade. The Lift blade also known as the 2 in 1, and the Mulching blade, also known as the 3 in 1.

Mulching is a pretty common feature on modern mowers, it allows the operator drop the clippings back onto the lawn instead of collecting them. Modern Mulching blades aren’t a true mulching blade, they are in fact a sort of hybrid, a cross between a lift and a mulcher. You can read more about both types here “Grass catcher troubleshooting”.

The type of blade is important, briefly, a Lift blade (2 in 1) is designed to collect grass, it does a really good job at leaving a clean lawn finish with no traillings.

The Mulching blade (3 in 1) is designed to collect grass or mulch the grass, whichever the operator prefers.

Mower lift blade

Lift blade (2 in 1)

So how do you identify them? The Lift blade will characteristically have large wings, and a smaller cutting leading edge.

Often referred to a s the 2 in 1 because it cuts and collects.

The Mulching blade, will have a much smaller wings and a much longer cutting leading edge. Most importantly of all, to make a mulching blade a mulching blade, the leading edge must be curved.

It’s often referred to as a 3 in 1, because it cuts, collects and mulches.

Mower Mulching blade

Mulching blade (3 in 1)

And finally we can get to the sizing. There are just three important measurements to get hold of. The overall length measured in inches, the diameter of the centre bolt hole and finally the blade boss shear pin locating hole distance.

The overall length is important, too short, and your mower isn’t cutting the correct swath, too long and, well, the blade just won’t fit.

The centre hole, now this is a critical measurement, and the one that can cause big problems if you get it wrong.

The centre hole of the blade isn’t just the bolt hole, it’s the balanced centre of the blade.

The shear pin hole distance is basically the distance between the centre bolt hole and the shear pin locating holes. These guys must be right or the blade wont seat on the blade boss correctly.

Mower blade length

Measure blade overall length

Mower blade centre hole measurement

Measure centre hole

Mower blade measuring Mower blade boss

measure shear pin holes

mistakes to avoid

The following are real dangers and mistakes that I see customers make every season. 

  • Fitting the wrong blade type – causing the mower to under perform.
  • Fitting a blade with a larger centre bolt hole, causing the blade to be off balance and cause excessive vibration.
  • Turning the mower over on the wrong side – mower should always be tilted with air filter side facing up, check out this post “Correct way to tilt your mower”.
  • Fitting the blade upside down – the blade wing tips point away from the grass. Some blades may have grass side stamped into the blade.
  • Over-tightening your blade bolt – when the blade is too tight, the engine may fail if the blade hits a solid object. Check out this post “Engine kickback”.
  • Turning the blade bolt the wrong way and damaging the threads. Check out this post “Blade bolt stuck”. 
Mower blades

Wing tips point away from the grass

Symptoms of wrong/damaged/badly fitted blade

The following symptoms are a sign of a possible problem with the blade assembly and should be investigated for loose or damaged components.

  • Excessive vibration
  • Constantly loosening blade bolt
  • Constantly loosening mower components
  • Knocking noise
  • Mower not bagging grass
Mower blade damaged

Damaged blade

Related Questions

Are lawn mower blades meant to be loose? No, lawn mower blades are meant to be tight. Use a torque wrench to tighten to manufacturers specification.

Auto Technician and Writer at | Website

John Cunningham is an Automotive Technician and writer on Lawnmowerfixed.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write "How to" articles that help fellow gear-heads with all aspects of mechanical repairs, from lawn mowers to classic cars.