Are all 1.5" Fuel Caps created equal?

[KnotConnected]

The fuel dock last year lost my fuel filler cap. I purchased the 1.5", part number 412439, which seems to fit the hole, but doesn't screw in as though the thread is wrong. Are all 1 1/2" fuel caps identical, or are there different varieties with different threading?

 

[Grub54891]

Yup, Some are different. Can't tell ya the thread count/taper, but one customer had to replace the whole assembly, as we ordered 3 different caps, and none would fit.