this is how i would do it
measure across the full width on outside of the blade, this is the diameter blade required
measure across the center hole this is the bore size required
the 2 measurements shown on blade above are teeth size and the blade thickness.
example of size's
185mm x20mm x2.5mm x1.6mm also available in
210mm diameter sizes
230mm diameter sizes
wirecutterman, December 2011