Yes it will fit the ASP FS91AR engine.That engine has a 5/16"x24 crank shaft thread which fits the 5/16"I.D spinner adapter ring included with this spinner.Adapter rings should be sold separately as well for those trying to fit other engines with different crank shaft diameters.
I was very surprised to see the quality of this spinner, it has a high sheen and the starter rubber does not stain it. It is well balanced and goes straight on to the prop. Just be careful that the aluminium does not touch the prop as it will damage the prop and weaken it. A very nice product.... Well Done HK
Nice spinner. But don't know what thread size the spinner mounting nut has. I thought it was M8, but it isn't. Didn't fit on my Zenoah Titan 20. Impossible to mount if you don't have the exact thread on your motor! Otherwise very nicely made and precise! APC 16x8 fits without any modifications.