Bonded Splice, For XR100 Series Rail. The BOSS™ (Bonded Structural Splice) provides a strong, bonded connection for XR Rails. No assembly, tools, or hardware required. The built-in bonding spring has teeth that bite into rail, creating a connection that meets all UL standards. he BOSS™ eliminates restrictions around splice locations. Place it anywhere along the span (except the outside cantilever).