The fitting that screws into the propane tank (P.O.L. Excess Flow Valve) has a left hand thread therefore will screw into the tank to the left, instead of most threads that screw to the right. It will screw into the inside of the propane tank valve. This P.O.L. fitting will fit any standard propane tank, however may not screw all the way into the tank depending on the style of tank that you have. Be sure that the P.O.L. fitting fits snug into the propane tank if there are threads exposed. You do not want any added fittings, regulators, gauges, etc. between your POL fitting and tank. The POL fitting will screw directly into the propane tank, left hand thread.
Instructional Manual here
View video here.