Miyata question
 

I've recently picked up a 1990 Miyata 721A. There is a braze-on on the underside of the down tube. Like a water bottle braze-on, but only one.

Looking through a catalog I found at: www.miyatacatalogs.com , I see that Miyata called it an "Air Bottle Basement".

What the heck is an "air bottle basement"??

it's for a c02 cartridge ... something about trying to appeal to the tri scene.