Abstract: Described herein, among other things, is an attachment system for connecting other accessories to the upright structures of a boat dock, deck or related systems, said upright structures comprising at least one post, a pair of tubular portions provided for interlocking together forming a tubular sleeve for application about the post forming the upright structure, said tubular sleeve provided for securement of other accessories thereto, to accommodate affixation of the other accessories to the post forming the upright structures for the dock or deck, and to prevent the untimely disconnection of the accessory from the post during its usage or storage.