If you can't get to the store right away to buy metal M8-50 (or 45) here is a printable M8-50 bolt and a M8 nut. I've made a special thread so its mor...e easily printable.
If making from PLA do not tighten with a hex wrench or it will snap the bolt, and cause you to have to drill out what's left in the handle (unless your gonna spend 3 hours making another). PLA+ might fare better, as well as PETG, let me know in comments if either of those can be tightened without breaking.
Be sure to print the bolt on a raft!