Flow Security SystemsLocking Filler Cap with Male Adapter | Designed to Secure Stationary Storage Tanks | Breathable Cap | Free Spinning Locking Design | 2” NPT Cap | FSS 720

I have an auxiliary fuel tank in the bed of my truck, that constantly feed my primary tank. I bought this cap because of the limited access to the full neck makes the food over style incomparable. I wound up making a gasket to semi seal the cap. Other that that, it does what I need.

There is no rubber gasket at the inside top of the cap. The fuel splashes out very easily and gets everywhere. I made my own gasket but it still leaks, just not as much. I use this on my truck-bed transfer tank. The item is heavy, tough, looks great, good concept but leaks way to much with regular stop and go movement. I did ensure I only filled the tank till it was several inches from the top to reduce splash leaks but that did not seem to help much. A simple rubber type gasket would fix the majority of the problem.

Like that no one can still my fuel

Bought two for one of our tug boats and a transfer tank. These work great. Vented. Dont get the other ones on here. These are the way to go......

Locking mechanism seems acceptable and can be tricky to lock. Looks good and seems to work as expected.

Surprised it doesn't have a gasket but I guess that's' how it vents. I'm on the fence if this will work for my vehicle transfer tank without overflowing while driving on bad roads/offroad. The product seems well built.

Locking Filler Cap works well. Looks like it was made well.

Used to lock secondary bung on diesel transfer tank, leaked fuel all over rear window, first speed bump when tank was nearly full