What are these little seatpost bolts called and where can I get one?

[Monkeeee01]

This be ok?

 

[averagebiker]

Try asking at your lbs if they have a nasty scratched up seat post in the parts bin you can rob a barrel nut off

 

[averagebiker]

This be ok?

View attachment 961405

Oooo, they look too nice to hide away under a seat lol