Are Lawn Mower Blades Universal?

Have you ever been mowing the grass and noticed a weird pattern emerging? That’s a sure sign your mower blades need sharpening or replacement. But good blades can be expensive! Replacement with a cheaper version or a generic model seems like the best idea, but are they universal?

Yes, you can replace a manufacturer’s mower blades with those of another manufacturer, provided the following match up with your mower:

  • Length
  • Width
  • Thickness
  • hole numbers
  • hole sizes
  • hole shapes 

Clear as mud, right?  Each mower manufacturer sets up their mower with a certain blade type in mind. If you can find a blade that identically matches the specifications of their blade, changing is fairly straightforward. However, the blades must match perfectly. Failure to match is a recipe for disaster!

Mower Blade Dimensions to Measure First

To determine what blades may work as a replacement, you first need to identify the dimensions of your existing blades.  You first need to check

  1. length,
  2. width,
  3. and thickness.

These dimensions vary widely from manufacturer to manufacturer, so accuracy in measurement is key in identifying the correct replacement blade.

  • Blade Length. Mower blades come in sizes ranging from 6” to over 32” in length. Getting the right length is important for safety. 
    Mower blades are measured like your television set.  Start at one corner and measure diagonally to the far opposite corner. For example, if you start with the upper left corner, you will measure to the lower right corner.
  • Blade Width.  Blade widths range from 1½” to 4¼”.  These are measured straight across, from the outer edge to the opposing outer edge. You measure at the widest (and flattest) location on the blade.  This is generally found in the center, right near or over the center hole of the blade.
  • Blade Thickness or Depth. Blade thickness or depth varies from 1/10” to nearly 1/3”. This measurement also runs outer edge to outer edge, straight through the blade itself. Identify your widest existing thickness/depth and measure at that location. If you are in the US, be sure to measure in inches, not centimetres!

Mower Blade Hole Configurations and Measurements

The mower blade holes are how the blades are attached to the mower itself. The configurations generally range from a single-center hole to a 3-hole system and come in a variety of sizes, shapes, and hole distances.

Center Hole Replacement Mower Blades

This configuration is unquestionably the easiest to identify the replacement for. A single hole in the center of the blade. That hole may come in the form of a circle, rectangle, 5-point, 6-point, 7-point star, bowtie, spindle, or even triangle spindle form.

Circle is the easiest to work with. Simply measure the diameter of the circle, and that is the hole size you use in identifying a correct replacement blade.

Rectangle is a bit of a misnomer. This will look like a rounded rectangle and will need a measurement of the diameter lengthwise and again widthwise.

5-point, 6-point, and 7-point stars do not have specific measurements. Rather, they are identified simply by the style of the hole. Look at the hole and count the number of outwardly protruding “points.” These points will be rounded but will protrude out from the center. The number of protrusions or extensions determines the number of “points” in the hole description.

Bow Tie is a little difficult to describe. It has points on either end, bulges out, then pinches back in, in something reminiscent of a warrior’s shield or a lady’s hourglass figure. This configuration has no measurements and is simply identified by name.

6-point Spindle is a combination of a 6-point star centered within a bowtie configuration. There are no measurements involved; this center hole is identified by its name alone.  

Triangle Spindle is an upside-down triangle, also centered within a bowtie configuration. Like several others, there are no specific measurements involved.

3-Hole Replacement Mower Blades

A 3-hole mower blade has additional measurements to be taken before you are ready to identify a suitable replacement blade.

In addition to your center hole, there will be holes (generally smaller) on either side of the center hole. You will need to measure the distance between those two holes. You measure center of hole 1 to center of hole 2. This measure will take you directly over the top of the center hole.

In some blades, the outer “holes” are not round holes, but rather elongated slots. These can be paired with washers to adjust for different blade styles.

The central hole can take multiple forms and shapes.

Some “universal” blades come with differently configured tabs to allow for modification to fit different brands of mowers.

If all this measuring is not your thing, and assuming you can find the model number of your mower, you can also Google “replacement mower blade manufacturer model number.”  For example, if you have a Ryobi RYAC130 13” 11 amp corded electric walk behind mower from Home Depot, it is simple to Google for replacement blades, and a selection of choices will pop up for you. 

Simply type “replacement mower blade Ryobi RYAC130,” and you’ll get over 9,000 results.

Assuming your mower is a fairly common brand, you should get equally good results for potential replacement blades. However, it is on you to make sure you order the correct item, so knowing what you are talking about will be helpful.

How to Replace Your Mower Blade

Each brand may have its own idiosyncrasies, but here is a basic outline of the steps to take to replace the mower blade yourself, saving money and earning kudos from the family!

  1. First of all, disconnect the spark plug to avoid any accidental startups while you are tinkering with the blade.
  2. Lie your mower on its side. You want it on the side that does NOT have the carburetor on it. Lying it on the wrong side can cause gasoline to spill out.
  3. Remove the fasteners that hold the current blade in place. Use one hand to hold the blade steady while removing the nut or other fastener type with the other hand. Most newer models have a single nut fastener.
  4. Remove the old mower blade.
  5. Install the new mower blade. Make sure all of the holes line up properly. Also, there is a “top” and a “bottom.” You must make sure the cutting edges are facing outward, in the direction of rotation. Otherwise, you will get plenty of spin, but no cutting action. Some blades now make it impossible to install the wrong direction, but not all are so kind.
  6. Take a few moments to look at the blade and consider the rotational direction before installation. If, after installation, you realize that the blade is not cutting properly, simply remove the blade and try reattaching with the edges turned the opposite way. Simple fix, and it should take less than 5 minutes to correct.
  7. Complete installation by reattaching the plate and fastener. Be sure to tighten thoroughly. Loosely tightened mower blades are not only ineffective, but they also have the potential to be dangerous, as well.

Final Thoughts

This is not brain surgery, but it does require some knowledge in order to be done properly. Replacing your mower blades, rather than taking it to a dealership or repair person saves you money, time and frustration.

If you’re unable to remove the fastener initially, try a little penetrating oil on the nut. Let is sit for a bit, wipe it off and try again. Sometimes manufacturers put those on really tight, so initial removal could be an issue.

Happy Cutting!

Peter Toth

Hi! I'm Peter, the owner of BackyardGadget. Working around the house has always been a big part of my life. I've created this site to share my experience, and to help people choose the right tools for the job. Thank you for stopping by!

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