Breather plug / bolt mag housing model D

Hi as above part number 11110112 is bolted to the magneto housing next to the grease nipple is it just a normal bolt as mine seems not to be a breather in any way ? Is it ment to be undone ( breather?????) when using the grease nipple to fill the main crank bearing to stop you filling the crank case then locked down when finished it's just the term breather that's confusing me .
Thanks for any help
Thanks for any help