I want to chase the threads on the bosses. Would anyone know the size?
Thanks!

it's a 6mmx1 Which is the standard 6mm coarse thread.

Thanks! BTW does it need to be a flat bottom tap or will a regular one work?

Woops I think I may have described the situation incorrectly. The threads I am referring to are the one on the boss that is brazed to the stay. Not the one that the brake is bolted to.

Bosses with a removeable post (often found on Al or Carbon frames, less so on steel ones) have been made with a few different threadings. Generally larger in diameter and with a coarser pitch then the M6 threads that run inside the pivot portion of a canti mount. As to the need for a bottoming tap- I would think it is obvious as to is the hole a through one or with a bottom (as in blind).

Didn't the bases come with their posts? If so then can't you measure the post? Andy

I I can't imagine a taper (starting) tap will work too well, you'll need a bottoming tap. Or maybe a plug tap will work. In any event, you probably are not going to get it locally unless you have an industrial supply.

It says M10 x 1.5 on paragon's site. There have been other sizes, but I can't imagine you having access to unbrazed bosses for those other sizes. M10 x 1.5 is the standard 10mm coarse thread.

Andy, they did come with posts but after we brazed them on the fork blades and seatstays they seem a bit "sticky". So I thought I'd chase the threads and clean them up.

if they thread in, being sticky is good. I thought they came with loctite on them. I would just put some grease on the threads

Unterhausen, thanks!! I didn't think to look at Paragon's site and that's where I got them! I checked McMaster Carr and they have the tap for $10. Works out as I need a few other things from them and their fulfillment center is only 30 minutes away.