Traditionally masts that are keel stepped had wooden wedges to support the mast at deck level because the hole in the deck is a bigger than the mast to be able to slide the mast through the collar easily and to fit through halyards and electrical wires, hoses and so on. The problem with wooden wedges is that they can leak and they can come loose, so quite a lot of effort needs to be spent to make them, to secure them and to waterproof the collar region. There have been some (in)famous mast failures where the wedges have caused the mast to break. In one case, the wedges worked free until only one wedge was carrying the load at the front of a mast collar and then this cause a failure in 40mm thick carbon fibre because the laminate was mostly unidirectional and had relatively low shear strength in a vertical section. Spartite on the otherhand pours in as a liquid form and whatever the rake, bend and irregularities of the collar it moulds itself to fit. It is a high performance cold curing polyurethane tooling plastic that has relatively high strength and negligible shrinkage during curing. It is able to provide a single mast chock that is reusable, that is a perfect fit and that is far cheaper and easier to make than trying to custom build individual wedges or to machine a chock from solid plastic plate.