What is the smallest hook size in an underspin?

I wanted something in size 6 or 8 maybe?

thanks

Probably depends on the underspin's weight, especially for commercial brands. You might be able to get those size hooks in a custom poured underspin. I know that a 1/16oz Roadrunner has a #4 regular hook & the 1/32oz Roadrunner has a #6 hook. I would think all the other brand's underspins would probably have the same hook sizes in those weights, but I'm not 100% sure about that.
Then, of course, there's underspins with sickle hooks, and sickle sizes are quite different in their "size rating" than a regular bend hook.

1/32oz roadrunner is pretty deadly for both crappie and bluegill. Total weight of the whole thing is about 1/16oz make is cast pretty good distance and can still retrieve very slow. Just ordered a couple of 4pks to replenish my stock. Also caught a few of 12” crappie yesterday under bobbers and swim slowly on bottom.
1/32oz roadrunner with trout magnet. I like to bend the hook point out a little when use with crappie plastic.

Thanks for the tip! I caught about #20 the next day!