458 Help on the name of this kind of nut

Bleeder screw?
You could probably thread in an ordinary bolt with some Teflon tape to keep it sealed but there’s air in the system now so that might not get you very far.

 

I believe it is a locking nut.

I assume you tighten the short bolt it prevent backing off?

 

That a D nut

 

I was waiting for the inevitable and much-needed deez nuts or (deez nuts-adjacent/equivalent) response. I was tempted to but stopped myself. I had a feeling you would be the one to deliver. Thank you.

 

Thank God someone picked up on it lol

 

Specialty part. See if you can get a replacement from Capistro or have a machine shop fabricate you one. Basically it is a cross drilled head of a short threaded bolt that attaches to the valve arm. It shouldn't loosen if it is bolted up tight. The long shaft pulls on the valve attached to the right angled short bolt and opens it. It is adjustable by threading assembly up or down on the long shaft. This is about the closest thing on McMaster Carr that possibly could fit, fwiw. https://www.mcmaster.com/products/threaded-rod-ends/corrosion-resistant-ball-joint-linkages/system-of-measurement~metric/

I believe simplest based on your location would be a machine shop to fabricate it for you, probably weld a pad on a bolt, cross drill it and tap it for the long shaft and cut to length the side arm. with the proper thread spacing diameter etc. GLWT.