You need to know the size of the shaft that the driven is riding on. I have no idea what you mean " buying it from blast led ". Whoever is selling it, ought to know the size of the shaft. FWIW, the shaft on the 40 series that I own is 3/4". I really doubt that it would be 5/8". That is the shaft size on a 30 series, which is smaller and a lot less robust than a 40.