Rocky's 313 #4 Permanent Reel System with 4" Hub - Rocky’s #4 Permanent system is designed to be bolted in place. This system can be used for a number of applications, including under diving boards. The #4 Permanent can be mounted in all kinds of ways (to walls, above ground pools, raised decking, etc.) providing versatility for uniquely shaped or positioned pools. This system uses Rocky's 12-sided, 4" anodized Commercial Tubing or Rocky’s 4" Adjustable Tubing.