Universals Standard Tubless or UST is a tubless standard developed my Mavic which features specifically shaped, square profile rim hooks which lock the UST tire bead in place creating an air tight setup without the use of sealant.
UST rims require the use of UST compatible tires for a sealant-less setup however non UST tubeless tires can be used as long as tubeless sealant is used. Only Kenda tires labeled UST will be UST compatible.