Depends on what you mean and what the different bikes are like.
If you really mean hub:
The hub is the center part of the wheel, that holds the wheel axle and the spokes, and in some cases the brake rotor.
Most 26" MTBs these days use dic brakes, while BMXes mostly use rim brakes. And to be able to fit a brake rotor to the finished wheel, you need to start with a disc brake hub, which a BMX hub is unlikely to be.
But using a rim brake BMX hub to build into a rim brake MTB wheel - no problem
Also, most MTBs use 32 spokes, while for BMX, 36 spoke is more common. You need to match hub spoke count to rim spoke count to avoid complicated builds.
If you mean wheel:
BMX regular size is 20" against MTB regular size 26". You'll get all sorts of troubles by dropping 6" from the wheel diameter. The bike will handle differently, and the pedals will drop a lot closer to the ground.
The hub is the center part of the wheel that holds the wheel axle and the spokes together. The hub off of a BMX cannot go on a 26 inch Jumper dirt bike, it will not fit.
24lbs is about average, but if you take off the brakes ect. it will make a big difference and take it down to at least 23lbs
freestyle, dirt, street
Street, dirt, vert, anything
The standard size for BMX bikes is 20-inch wheels, which makes all frames pretty much the same size too. Decide which kind of riding you want to do, dirt/race, vert or flatland/street, them take it from there. If you intend to use the bike to ride around in traffic and actually going places, don't get a BMX at all. Get something with a more sensible riding position and some gears.
16 inch is 40.6 centimetres.
no bmx bikes hndelbars are 22.2 mm and mtb dirt jump are 25.4 mm. the dmr swarm stem is ment for mtb dirt jump bikes (25.4)
if you want a bike for trails and dirt go for an eastern trail digger or a fit bike
A BMX rider from Missouri who rides for dirt bros.
A 20 inch tire.
no but you can get a dirt bike or a cruiser bike or a speed bike but i havnt seen a bmx bike yet.