The FSS-754 Versalock security cap is a quick and inexpensive way of safeguarding costly fuel and oil from theft, tampering and vandalism. It is designed for use on mobile fuel transfer tanks as well as above ground commercial gas and distillate tanks. The FSS-754 uses built in valves to equalize the pressure and vacuum. It also incorporates Spinsecure's patented "free-spinning" technology, its 1-piece (padlock free) design eliminates torque points making it virtually impossible to remove without the key, most tank lock caps use a simple padlock which can be broken, cut off or leveraged with a crow bar. The FSS 754 secures to the filler neck and will free spin until unlocked.