By USA Mower Blades
Most lawn mower blades have a round center hole that is used to connect the blade to the spindle. When the center hole is round, matching a replacement blade is relatively easy. Simply measure the inner diameter of the hole. If the original blade has side holes (smaller holes next to the main center hole), be sure to take this into account. Side holes will almost always be round. If the original blade has side holes, the replacement blade must also have side holes to attach securely to the spindle.
These outer holes are measured two different ways— individual diameter and the space between the holes. Measure the inner diameter of the side holes the same way as a center hole. The correct way to measure the distance between the outer holes is from the center of one hole to the center of the other hole.
Other popular center hole designs include 5-point star, 6-point star, 7-point star, and rectangular.
5-point star, 6-point star, and 7-point star center holes will not have a measurement but will be denoted by name. These blades will fit the specific matching spindles. Some blades will have an H-pattern or bow tie center hole. This type of center hole will fit 5-point, 6-point, and triangular spindles. H-pattern or bow tie center holes will also not have a measurement.
Rounded rectangle center holes will typically have two measurements, inner length and inner height.
For more information about USA Mower Blade or for help measuring or determining replacement blades, please call customer service at 800-444-7856 or by e-mail here.