Edson Marine XL PowerKnob Strap:

Edson's PowerKnobs are equipped with two straps that fit wheels with diameters from 5/8-inch to 1-1/8-inch.  But sometimes the wheels rim is slightly larger and not perfectly circular so Edson now offers an extra large strap that will allow you to attach an Edson PowerKnob to a rim with a max circumference of 3.75-inches!  

 EB414 - PowerKnob Installation Instructions - Manual