you take a piece of stianless pipe with the same id of your shaft tube, split it in half then weld tabs on both sides and drill for bolts. then weld the holding block onto that piece and it will clamp around it, works slick.
It's very sharp under water when one dives down to take a look at things halfway through the season too, isn't called a "razor" for nothing after all. I doubt spurs would contend with deck mats that a deckhand liked to wash by tying a rope to and let dangle over the transom just waiting to be backed over.
i put 6 , 4in. s.s. razor sharp discs ,ahead of the donut shaped zincs for line cutters one year and all 6 props showed wear just outside the hub on the lead edge from cavitation .called everyone that had them installed and told them to take them off because of the prop wear factor. can,t remember the name of the manufacturer, but used to advertise in the natl fisherman and commercial ffisheries news. have not seen the ad since 2004! maybe 2003.
Thats some great video of rope cutters,I have never heard of the other two scissor cutters.I know I have had spurs for 20 years and have always had good luck with them.i have replaced a number disc types for people with spurs.The disc type increase the hub size of your wheel,causing a small cavitation at the hub.