The Covermate III Cover Lift is ideal for spas and hot tubs with a deck built around them that is to or near the top of the hot tub skirting. this hydraulic lift utilizes an exclusive windlock system that virtually eliminates broken shock syndrome. The CoverMate III Deck Mount is for Hot Tubs with a deck 0-4" to the top of the hot tub skirting. Spas with the deck 5" below the top of the hot tub skirting can use the standard Covermate III. The Deck Mount CoverMate III will not work on round, hexagon or octagon spa cabinets or on hot tubs with a corner radius of more than 12". - 4 per case