Garelick Low Profile Seat Slide and Locking Swivel Features: Allows helm or boat seats to adjust fore and aft; Slide mounts under seat in between seat and pedestal base; Convenient handle provides solid locking at any position; Compatible with most 360 spiders; Wobble-Free Design/Operation; 6" Travel, standard size for wood or plastic seats; Anodized aluminum with stainless steel hardware. Spider swivel casting not included; Specifications: 7.5" (19cm) Fore and Aft Travel 8.5" W x 8" L x 4" H (22cm x 20cm x 10cm)Assembly & Installation Instructions