I am tall so used just the main block without the two spacers. It needed some minor trimming so it would fit deeper in the bow. It is a snug fit in my 4Fun, but can shift slightly when pressing with one or both feet. This product did NOT come with velcro, as J.L. promised. It is unlikely it will come out during a swim, though.
Third Time I've Purchased This Great Product
Posted by G. Baldwin on 19th Jun 2012
Without making any insinuations about what they replaced, this is the 3rd set of Jackson footblocks I have purchased, and all have worked out perfectly. I have always had a problem fitting my feet into low volume boats, and these footblocks are a perfect solution. I strongly recommend holding them in place with some velcro on the bottom attached to velcro stuck to the hull in the bow.