Summary

This design is meant to protect gas cylinders from getting their threads/ ports plugged with debris or damaged.
The difference between this design and the other one on my profile, is that this one comes with threads which are optimized to fit a Propane/MAPP cylinder properly with minimal effort to get it on the first time. I tested it by running water from my tap onto it and checked the innermost threads/ top of cylinder to find that they remained dry. This is not to say my design is waterproof, but will certainly repel water from most situations, and dirt/debris/damage to the threads.
Because this one is threaded for gas, it will not fit onto an Oxygen cylinder.
Knurling on the outside makes it easier to grab
And of course it is tight enough that I can carry it by the cap.