Invented by ironworkers and construction safety professionals. One standard size mounts to any beam over 4" top flange (up to 21/2" thick) for safety of workers walking or working on beams and girders. Users attach shock-absorber lanyards and walk the beam to connect iron, set joist, install studs, rebar edge protection, etc. Good for up to two workers in each section. May be used 10 to 60 feet between posts.