Ball clamp

EDIT: Don't print this thing - it does not work, because the clamp has too much flex. Maybe with a lot of infill...?

I had trouble printing this with a brim, so I used a raft instead. But maybe a brim might work for you.
Print both parts lying flat (like in the first image).

Although the item works fine, I might redesign the closing mechanism because the clamp doesn't hold the pin as tightly as intended.