Where did this bolt come from?

[JolllyRedGiant]

Whilst taking the wheels off to get at the brake pads on the rear of my 540i, this bolt fell off and I cant figure out where it is supposed to go. Any help is appreciated.
bolt.jpg.

[Twistytee]

I’d venture to say that’s not an OE part. It’s a locking castle nut with cotter pin. Commonly used in SAE applications like wishbones and trunions on Brits. BMW uses metric self locking hex nuts. Maybe the PO used one from his spare parts bin?

[JolllyRedGiant]

Would make sense that its not OE cause it came off from just me kicking the tire and i couldn't find one like it on the other side.

[geargrinder]

Herrrrmmmm... Yeah that looks like it came off the wheel bearing retainer for my old boat trailer. Or the rear axle nut off my mini-bike I had when I was 13.

Are you sure it wasn't just knocking around on the ground where you were working?

(PS: also - pro-vocab-tip - that's a nut not a bolt).

[StephenVA]

Nut jab this early?

Tie rod castle nut with cotter key. Check the treads and you will see they are SAE not metric. I vote for on the ground as the cotter key was pulled out from the hole not broken off.