The Trex500 Flybar lock is a tool used during set-up. To use this tool you would first remove the head button, then bolt the flybar lock in place using the head button hole in the head block. At this point your flybar will remain level at all times, allowing you to check/set collective pitch and cyclic pitch. This tool allows the flybar to rotate but not flap. It also allows you to rotate the mainshaft with the lock intsalled. This tool offers so much freedom, it is possible to fly the heli with the tool installed (however, strongly not recomended) We have done this by mistake and gives new meaning to the word "Pitchy".