I'm confused i thought in mtb'ing, there was only one type of bottom bracket thread. Yet i have seen a frame advertised as having a american bottom bracket. What does this mean?

One piece crank innit. A crank that's one big piece of bent metal and seperate bits to each side of the BB, a bit like outboard bearings.

typically seen on BMX's.

rigt. so i would need new cranks if i were to buy this frame. are they any good? and any examples?

I've had a thought and it may actually mean three piece cranks.

One piece cranks are a bit rubbish, and it's probably not them. Three piece cranks rock hugely, you'll not find anything stiffer. Huge great irons of cranks connected by a 1 inch thick rod of steel with lots of splines typically. They're usually pretty heavy, but great for tough mans work.

I had some cranks on my gimp like this, they were very heavy but so stiff!

Its a big threadless shell.you can fit press (or stw hammer) in cups with loose ball bottom bracket sets or if its a profile/redline 3piece crank then you could fit a few sealed units that were made for those cranks.a 1 piece crank along with a 1 piece bb unit can also be fitted.bullseye made 2 piece cranks come to think of it.so 1,2 or 3!

dmr do a kit called wonder cups that press in so you can run an mtb bb unit in there.go for the mrk2 version if you want to run HT2 style units in there as they have a revised face on either side that will make the outboard bearings fit correctly.

A fanny bracket?

lol

samuri might well be right but it could be just that it has a 73mm shell
yknow like a spesh or a trek or a yeti.
used to be the term used for it when god was a kid.

'an american bottom bracket' – one yank and it comes off?????
Ahhhh… no, that's an american bra…..
sorry
Q