I should know this by now, but I wanna make sure. What would I need to use a bmx crank on another type of bike, like a fixie or mtb? I know they usually come with ashtabula/american bbs(usually the cheap or bso) and english bbs. And are there possibly other types of splined sprockets that might work, since it seems like most don't seem to be bigger than a 38t or so.

Curious why you would want to use a BMX crank on a not BMX bike? Plenty of great fixed gear and single speed cranks and even more MTB cranks. I would only want to use a BMX crank on a BMX bike unless for some reason I had an extra one and really had to use it for this. I see no real advantage to a BMX crank anywhere else.

Interested in this thread because I do have a spare bmx crank from my dumpster find bike. I'd use it on my Diamondback MTB bmx conversion. The DB has a square taper and the BMX is splined.
Is this a feasibe thing to do? I'm sure it'd be more economical to just get a square taper single but a project isn't always cost effective to get desired results
BMX axle set-up like this, 8 splines.

What I've found is I would need something like this...

Because I like how they look. I already have three ashtabula bmx sets, two of which are going on cruisers. I don't see a reason not to do it, unless I can't find the chainring size I want, people use bmx parts on not bmx bikes pretty often.

Looks feasible to me. One of the ones I have looks like the one up top, but it's for an ashtabula/american bottom bracket, like beach cruisers typically have. It came off this funky Specialized bmx bike. Regular 3pc cranks are English bottom brackets. The other two are basically three piece american bb sets that use ashtabula chainrings.

I have a Giant Rincon mtb I converted to single speed, and I want to put one on it if I can find a 48t chain ring.

Ashtabula doesn't belong anywhere except the annals of history. Maybe a good idea back in the day before they figured out square taper/splined and then external bottom brackets but I wouldn't waste the time and money trying to adapt an outdated standard to a modern bike. There are some conversions from Ashtabula to English threading but I have not really seen one to go backwards because you cannot do so in an English threaded bottom bracket and nobody would buy a T47 bottom bracket shelled bike to put some outdated cranks on.

Plus Ashtabula would not be very sturdy or strong for mountain biking hence why you don't ever see a real mountain bike with them. Certainly wally-mart specials that say not for "off-road usage" but there is a reason for that.

I think you're missunderstanding me a bit, which might be my fault. I'm not trying to fit ashtabula cranks to a bike with an english bb.

The three I currently have are ashtabula style bmx three piece cranks. They came from bmx bikes that are basically... either high end cheapo bmx bikes, or mid level bmx bikes. I don't know how to place them. But all three bikes they came from had american bbs.

One of them came from this weird Specialized bmx bike, that wasn't a regular tube frame bike, it had this weird space frame. It had a bb that looks like the one in that guys first picture; two sealed bearings you press in after removing the bearing cups, a splined axle with a nut on one side. It uses a typical bmx chainring.

The other two came off what are best described as bso bmx bikes. I think one was a Mongoose, maybe both, but one was spray painted. Their cranks were basically 3pc ashtabula cranks. Picture a regular ashtabula, except the crank arms slide on. The axles on these install just like a regular ashtabula crank
found a picture of what I'm poorly trying to explain. They are these style conversion.

Although the one I took off the Specialized is going on a klunker, the other two are not going on anything I intend to offroad. One is going on cruiser that I'm converting to a freewheel, sort of like a strandie. What I want is what that other guy wants, a bmx crankset for an english bb, not a downgrade to any kinda ashtabula. My Rincon is one of my street fighters, it's got a 48/16 ration and rides on narrow street tires. I also have a LaJolla which I was also considering slapping one on—it also has an english bb.

Sorry for all the confusion about it all. I was just trying to explain what I had versus what I was looking for.

Ok good because fitting an Ashtabula is silly but I would just go with a regular crank that makes your life way easier and you can find more chainring options for mountain biking rather than cranks designed around BMX which is a very different sport.

The klunker is a single speed—will be. I was thinking like a 38/17 for it, within what I can usually find for bmx chainrings. For the Rincon I'll take your advice, I've never seen bigger than a 40t in general searches. I might look at fixie cranks for that one. I've seen bmx looking fixie cranks, but they all seem to be like hollowtech sets.

External bottom bracket cranks are so much easier generally especially with Sugino and some others you don't need specialized tools to remove them and they are a much better attachment system. I was a square taper till I die person till I finally tried some Shimano cranks and had to install them and then was working on them more often and boom it was a game changer. No more crank pullers? Sign me UP! I still have a bike with a square taper crank that is a single speed but beyond that I think pretty much everything else is external BB mostly 24mm but have a new Campagnolo crank which is different.

I would get a crank you need to fixie in anyway though a single speed or fixed gear crank could work assuming a 68mm bottom bracket and enough clearance (as track bikes are 120mm and QR MTB is 135).