BB sizing help!
 

I ride a 29er single speed mtn bike and I'm looking to upgrade the crank and BB. It was recommended to get the BMX Redline Flight crank and BB (I'm a big aggressive rider). I'm doing some price shopping and I'm not sure how to determine what Rebline Flight BB to get. My bike has a 68x118 but when shopping for the Redline BB it says the size is American 19mm spindle? Will that work? What do I need to know to get the correct size? Thanks!

they may mean the diameter of the axle,, metric system has been resisted in America , so as to be a rather oxymoron.

the 118 is width of the BB axle , but may no longer apply..
now the new external bb cranks have the spindle as part of the right crankarm.

Seattle bike supply is the Importer of Red line stuff , ask your Dealer for details..

19 mm refers to the diameter of the spindle. For BMX, they come in 19 and 22 mm versions. The BB bearings are specific to the axle size, but they all fit the same frames. All the modern BMX bikes round here seem to use the press-fit "mid" BB bearings. Threaded bottom brackets are referred to as "euro" BBs in BMX, so that's probably what you're after if you're fitting them to an MTB.

You don't want "American" bottom brackets, make sure it's a Euro, and as Airburst said, 19mm is the spindle, so make sure the crankset's spindle size is the same as the bottom bracket's.