The #17S has the same mounting platform as the #17, measures 1-9/16″ and was developed for small pocket scopes and laser attachments. The standard Picatinny rail width channel allows secure laser or night vision optic attachment at two points.
Two (2) solid attachment feet on the right side are firmly held in place with the A.R.M.S. steel locking foot and lever on the left side. A number of bipod manufacturers make bipods specifically to attach to the ARMS #17 or LaRue LT271 (which is made under licensing agreement with ARMS). Specifically, Magpul and Atlas make a bipod ready to accept the ARMS #17 or #17s. The #17 is a little larger, measuring 2", so in some ways, the 17s gives you more flexibility.