I have been looking and have not found what I want. I have the newer DDM overflow tank and it has a 32mm neck. I already spoke to Dave @DDM and he told me the size. Said pretty much any Honda one will fit and that it is 32mm. I want a round cap that will fit and I have found covers for the stock one, sticking out to much will give clearance issues where the line comes into the neck. The stock on just makes it by. Thank you in advance for your info. (While writing this I am trying one more cap that doesn't have that step piece, fingers crossed)
Cover for stock cap will be too wide as the stock cap just clears the inlet hose and threaded end.
This one hits on the bottom outer edge step and I would have to turn it down on a lathe. A smaller Outer diameter would clear. I am hoping to find one that someone found that just works.