These look like they would accept bullet connectors of some kind, but I can't seem to find the parts to actually look up what they interface with.

 

Looks like standard test lead ends, many sources.

 

Looks like standard test lead ends, many sources.

View attachment 297724

It's much smaller than a standard banana plug that most multimeters and such use. Is there another size that I'm unaware of?

 

There is mini-banana plug, Mueller Electric etc.

 

There is mini-banana plug, Mueller Electric etc.

Did not know that, thank you

 

I believe they are called tip jacks and plugs. Used on some smaller multimeters.

 

Phone tips. Used on old school headphones (like Trimm Featherweight), and probably telephone gear. Here's an example with dimensions:
https://www.keyelco.com/product.cfm/product_id/3145