What are these for exactly?
i know when i will unscrew it the bolt will break...
need to have it or can live without?

Its used to help keep the drive grounded. Used in conjunction with a Mercathode
Do you plug into shore power?

most of the time on trailer at home yes
10 -12 times a year when boat is in the water overnight and i sleep in it

other wise it never left in water

so...???

Figuring you've had the boat for a while and do regular maintenance. During maintenance have you ever found parts of the drive being eaten away, if not then your doing fine
Do you have a Mercathode installed?
If so then its doing its job, if not then guess your still doing ok

This is what can happen to a drive given enough time and galvanic corrosion

Dude, keep mercathode working, its a painfully simple system. Especially if you ever run in salt water. I think it makes a difference even in overnight stays.

Official Name : Continunity Washer. The screw thread is 10-34, if you want to drill it out and re-tap.

Oups…. My Bad …….10-24... No coffee yet !!!!!

thanks for that info will need it for sure!