The 115 Balance Rail is specifically designed for the BTX/ATX with a 115 mm objective lens. The Balance Rail attaches to the bottom foot of the optic and supports the objective lens and eyepiece for a much more solid base. The bottom of the rail is already contoured to fit Arca Swiss style heads but if you are using another adapter type, you can use one of the four 1/4-20 holes on the bottom to attach your quick-release plate. At only 2.75 ounces, once it's on, you won't leave home without it.
The Balance Rail will work with a 1.7 ME attached. All mounting hardware is included.