Attempting to build a custom brake system using metric bladder fittings proved successful harder than I thought. One of the last things I needed was a 12mm to 10mm adapter. It looked like that, but unfortunately it wasn't. While the male and female threads were correct, 12 turned out to be a bubble and 10 an inverted flare. Using a 21/64" drill bit, I machined the tapered saddle into a concave profile that would work for the job. Bubble ends seem to be the trend with modern systems and I was hoping it would be easier to find adapters. get a tee from Latvia, that's all. It can be made to work, but you don't have to.