Are Lawn Mower Blades Reverse Thread?

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Lawn mowers require regular maintenance, and part of that routine involves cleaning, sharpening and replacing the blades. To do this right, you have to understand how its blades are thread. This can be confusing so I will explain it in simple terms.

The nuts on most lawn mower blades are reverse thread to keep them in place. Since the blades move in a clockwise manner, the reverse thread keeps the blades attached to the drive shaft.

Do All Lawn Mower Blades Have Reverse Threads?

Lawn mower blades are not thread, but the nuts securing them are usually reverse thread. Note that I say “usually”. Some lawn mower blade nut threads are normal.

Regardless of the direction, nuts have threads to keep the blade from flying off. Nuts with reverse threads tighten the blade onto the drive shaft. Even when the blades turn, the nut keeps it from getting loose.

What this means is that reverse thread blades are non-existent, because the threads are on the nuts. Strictly speaking, lawn mower blades like those on the Craftsman M105 cannot be reverse thread because they do not have threads. But if one thinks of the nuts as part of the blade, then yes, most have reverse threading.

How to Know if a Lawn Mower Blade is Reverse Thread

If a lawn mower blade turns counterclockwise, its nuts are reverse thread. What happens is that when the blade turns, the nut tightens in the opposing way. This minimizes the chance of the blade rattling or splitting off, which can be dangerous.

There are other ways to determine if the nuts have reverse threading. One method is to check the discharge chute angle. If it is on the left, the thread is reversed. But if the chute is situated on the right, its nuts have reverse threads.

Another way to find out is to loosen the bolt with a socket wrench. If the socket wrench turns right, the nut has reverse threading. If the wrench turns left, the thread is normal.

The quickest way to find out is to check the owner’s manual. As mentioned earlier, not all lawn mower nuts have reverse threading.

For instance, a lot of John Deere, Cub Cadet and Troy Bilt lawn mower blade nut threads are not reversed. Craftsman lawn mower nuts are reverse thread however.

The point is that lawn mower blades have different setups. If you are not sure, the owner’s manual will provide the information you need.

How to Remove a Lawn Mower Blade

Lawn mowers are versatile. For comparison, check out this post on lawn mowers vs. weed eaters. But they need working blades to function. Yes you should sharpen the blade regularly, but at some point it has to be replaced. If the blade is bent or chipped, no amount of sharpening is going to help.

What You Need

  • 16mm socket (check the manual for the right size)
  • New lawn mower blade (if you are replacing the current one, make sure it is compatible with your model). The Maxpower blades are compatible with many Troy Bilt models.
  • Breaker bar
  • Putty knife or scraping tool

Step 1

Wear a pair of gloves. You must always take precautions when handling blades. Now you have to disconnect the lawn mower from its power source.

If it is gas, disconnect the spark plug and ignition coil. For extra safety, empty the fuel tank.

For electric lawn mowers, turn off the power and disconnect the power plug.

If you are using a cordless lawn mower, turn off the power and take out the battery.

Step 2

Turn the lawn mower over so the air filter and fuel tank are facing up. You should be able to see the nuts that hold the blade in place.

Use a wrench to take the nuts off. Take note how the blade is positioned because you have to place the new one in exactly the same spot.

If you are having trouble removing the nut or bolt, use a breaker bar. It is all right to apply some force.

Step 3

Turn the socket counterclockwise to loosen the bolt. You are doing it right if the blade turns with the bolt. Hold the blade with one hand while you use the socket. This is why you need to wear gloves, to safeguard you from cuts.

Clean the mower underside after removing the blade. Use a scraping tool, knife or other tool. Put the new blade on. Put the bolt back and tighten it.

How to Remove a Stuck Lawn Mower Bolt

It can be very frustrating to try and remove a stuck lawn mower bolt. There are a number of ways you can remove it, but I will stick with the simplest and most effective.

Start by disconnecting the spark plug and ignition coil. If you are using a cordless mower, disconnect thee battery.

Turn the lawn mower over until you see the blade. Apply WD40 on the bolt. Use a wire brush to get rid of the corrosion.

Give WD40 time to settle. Now use an impact wrench to pry the bolt loose. This should be enough to remove the bolt. If not, apply more WD40.

Safety Guidelines

Do not skip the part where you disconnect the lawn mower from its power source. If possible take out the battery or empty the fuel tank. You can never be too careful when it comes to handling blades.

Earlier I pointed out that you have to flip the mower over so fuel does not leak out. An even better option is to drain the fuel tank.

Always wear gloves when handling blades or any sharp objects. You might also want to put safety goggles on for fuel spill protection.

How to Tell Which Lawn Mower Blade Side is Up

The bent, dull edge is down and should face the deck. The sharp, tapered edge should be up and face the ground.

If you have enough experience with lawn mowers, you can easily tell which side is up and down. But even if you are new, there are simple ways to figure out which way lawn mower blades are supposed to be.

Look for a label on the blade that says “cut grass” or side down”. This makes it easy to determine which way to install the blade.

Frequently Asked Questions

Which way does a lawn mower blade unscrew?

The majority of push lawn mower blades turn clockwise. That is, when you are standing behind the lawn mower, the blade turns to the right. To remove the blade screw, turn the nut or bolt counterclockwise.

There are exceptions to this of course. But in general you can expect lawn mower blade screws to rotate right.

What socket wrench size do i need to loosen a lawn mower nut?

The easiest way to find out is to check your owner’s manual. Its Most lawn mowers use a 3/4, 5/8 or 1/2 inch head, but yours might be different.

Once you have the right socket wrench size, put the wrench on the bolt and turn it counterclockwise. If the bolt is rusty you’ll need to apply force.

Does my lawn mower blade rotate clockwise or counterclockwise?

If the cutting edge is on the right, the blade turns clockwise. You can confirm this by looking at the discharge chute. If the chute is located to the right, the blade moves clockwise.

How do I know if I installed the lawn mower blade correctly?

The most obvious sign is if the mower cannot cut grass. If you installed the blade upside down, your lawn mower cannot cut.

If you suspect this is the case, turn off the lawn mower. Disconnect the spark plug and ignition coil, or if you are using a cordless model, take out the battery. Check the blade if it is upside down. The sharp edge or the one with the label should be facing the grassy surface.