Great alternator very pretty, Can you please explain what drilling it out is?

Great alternator, wasted 51$ doing next day air shipping since I needed it immediately, arriving 3 days later.

Had to drill out the threaded hole w a 3/8 bit. Also the adjustment thru nut barely threads on but its tight and should be ok. If it has to come off again I would dremel that ear down on the alternator as its about an 1/8inch too fat compared to OEM or a remy reman. Part arrived new.