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Are Lawn Mower Blades Universal (Don’t do it!)

By: Author John Cunningham. Published: 2020/01/27 at 10:03 am

A new blade can make a huge difference to the performance of your mower and the quality of the 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? Lawnmower blades are not universal; they are mower-specific. A mower blade must be an exact fit and torqued to the manufacturer’s specification.

I’ve been 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.

If you need video help, check out “Replacing mower blade video” in the mower repair video library. It walks you through the whole process, inspecting the blade and blade boss, removing the blade, sharpening, balancing, refitting, and torquing the blade bolt to spec.

Torque blade to spec.

Ordering The Correct Mower Blade

Ordering the correct blade is obviously the first important step. Getting this wrong can lead to an ill-fitting and dangerous blade. Luckily, Identifying your blade is easy, there are a few ways to go about this.

Mower Make & Model

Order a new blade by make and model; 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.

Make and model number label

If you do have a label, inputting the make and model numbers on Amazon will likely give you a list of suitable blades. I like to use genuine parts if possible; the fit and quality are usually best. A good seller will list the part number, which brings us to the second way to identify the correct blade.

Blade Part Number

Blade part numbers

Every mower blade has a part number stamped into the body. 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, years of grass clippings and corrosion, etc.

Check out the Amazon lawnmower blade link below.

Amazon Lawnmower Blade

Blade Sizing

The third way to order a blade is by sizing it. I’ll often have no choice but to size a blade, as customers will just walk in with the 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 fitted.

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

Mulching is a common feature on modern mowers; it allows the operator to 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; a Lift blade (2 in 1) is designed to collect grass; it does a really good job at leaving a clean lawn with no trailings. The Mulching blade (3 in 1) is designed to collect grass or mulch the grass, whichever the operator prefers.

So how do you tell a Lift from a Mulcher?

The Lift blade will characteristically have large wings, and a shorter cutting leading edge. Often referred to as the 2-in-1 because it cuts and collects.

Lift blade (2 in 1)

The Mulching blade will have 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.

Mulching blade (3 in 1)

And finally, we can get to the sizing. There are three important measurements to note:

1 The overall length measured in inches – 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.

2 The diameter of the center bolt holeThe center hole, now this is a critical measurement. The center hole of the blade isn’t just the bolt hole; it’s the balanced center of the blade.

3 The blade boss shear pin locating hole distance – The shear pin hole distance is basically the distance between the center bolt hole and the shear pin locating holes. These guys must be right or the blade won’t seat on the blade boss correctly.

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 underperform.
  • Fitting a blade with a larger center bolt hole, causes 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”.

Wingtips point away from the grass

Removal and fitting are all covered in this video “Fitting a mower blade”. You may also find “Setting a torque wrench video useful.”

Symptoms of Wrong / Damaged / Badly Fitted Mower Blade

The following symptoms are a sign of a possible problem with the blade assembly and should be investigated for loose or damaged components. Check out blade maintenance tools here; they make the sharpening and blade-replacing process almost pleasurable.

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

Damaged blade

Related Questions

Are lawn mower blades meant to be loose? Lawnmower blades are meant to be tight. Use a torque wrench to tighten the blade bolt to the manufacturer’s specification. Overtightening a mower blade is bad also; it may cause engine damage.