So I bought a pair of 139 mids and it seemed like the kingpin nut wasn't staying tightened, seemed like my one truck would loosen by itself (even after tightening it down enough so that it wouldn't normally loosen by itself). Basically, I would see the kingpin nut at one position during the sesh, then look down at it, say, half an hour later, and it seemed to be in a totally different position, which bugged me out.
I chalked it up to a defective pair (?), and decided to try another pair- this time, 149 mids:
On this pair, to make sure nothing was just in my head, I marked a line in sharpie at "12 o' clock" on the kingpin nut after tightening the trucks enough to make sure the kingpin wouldn't (normally) loosen by itself . Sure enough, by the end of the second session with the 149s, the line I marked was now at around "8 o' clock". I did not touch the kingpin nut with a tool throughout the entire session. The weird thing is, I'm not even sure if my truck feels any tighter/looser on the 149 with the kingpin nut rotating by itself.
Is this somehow normal? Or did I just get really unlucky with two consecutive defective pairs?