John Deere blade nuts come in several sizes, depending on the model of lawnmower or tractor you are using. For example, the standard size for newer models is a 1/2 inch nut. However, older John Deere models use either a 7/8 inch or 3/4 inch nut for their blades. You can measure your current blade and compare it to these standards to find out what size your John Deere blade nut needs to be. Additionally, when replacing the blades on any John Deere mower or tractor, you should always make sure that the blade nut size matches with its corresponding bolt thread diameter measurement. This will ensure that your new blades are secure and won't fall off during use. To sum up, there are several different sizes of John Deere blade nuts available but typically modern machines require a 1/2 inch nut while older ones may require either a 7/8 or 3/4 inch one - so make sure to check carefully before purchasing replacements!