I need some help locating a seat binder bolt for an ‘86 Schwinn Peloton frame. The existing bolt is shown on the photos & the problem is that the bolt can’t be tightened fully because the straight knurled nut begins spinning in its recessed hole. I tried using a chainring nut wrench to hold it but that wouldn’t work because the bolt threads are almost all engaged and the center “point” of the wrench won’t let the outer ears engage (also tried a straight blade screwdriver without success). The thread diameter is 6mm, the bolt head is 9.8mm, and the nut is 10.1mm. The nut and bolt head tuck away nicely into the clamp and I would like to keep that look if possible. Most of the replacement ones I can find have an 8mm smooth outer section like that shown below and won’t fit into the short recessed areas on the frame and I don’t want to drill out the main bolt hole to allow it to fit. Anyone know where I could find a replacement bolt assembly or even just a straight knurled nut? I thought about JB Welding the nut in place but fear that won’t be able to take the shearing force of tightening. If it is one of those hen’s teeth old bike parts I will probably find a long enough bolt and a nylock nut to clamp it and the hell with the aesthetics. Thank you for taking the time to read this and for any suggestions/knowledge you can impart to me!
PS I am soon off to work and won't be able to look at any replies until later today so if anyone needs more information I am not being a jerk in not replying quickly. John

Maybe not a permanent solution, but I’d cut a slot perpendicular to the borked one, “customized” to your screwdriver or whatever other tool you might use to hold it in place.

I put a standard nut on a bench grinder, sized to fit tight. If the bolt head is too big, same grinder or a file.

I have many times used LocTite to prevent a binder nut from turning in it's bore. Never failed.

Since the inside of the bore might be painted and/or greasy, clean the parts well and perhaps allow the installed nut to cure for a couple of days before turning the bolt again.
Heat greatly accelerates the LocTite's curing time, even a hair drier can get the clamp hot enough in ten minutes.

Lubricate the bolt threads with good grease to reduce the turning torque exerted on the nut during bolt tightening.

I have purchased many on Ebay.

They are about $5.00 and come in different length bolts.

Buy at least 4 so you have them.

My bike shop friend binder bolts do not last that long

OK, dumb question maybe: I am familiar with LocTite thread lock, but not following how that will hold the nut in place. Are you referencing another of their products?

I'm assuming here that the nut fits into a recess in the seat lug ear(?).

The LocTite will wick readily into the space surrounding the nut's knurling. The cure rate is slower when the inside surface of the binder's socket is painted, but as I said, heat helps.
Epoxy would also work.

I much prefer the existing bolt to a more normal binder bolt because your standard grade-8.8 socket-head bolt is practically immune to breakage versus any shoulder bolt in my experience. And the LocTite is much cheaper than any bike-specific bolts.