What you're calling the H style is actually what is called the V style for high volume here in America. These actually came out of Europe and Milton decided to name them the "V" style. Oddly, and fortunately, all V style are interchangeable. The Flexzilla couplers will work with Milton V plugs and visa versa. Likewise for the Prevost high flow. When it comes to couplers Provost is the nuts. The Milton V couplers don't last very long. The Provost last forever.