I was just thinking that's probably a M6 screw. A 1/4"-28 is just a little bigger. My chart says a #3 drill bit for the 1/4-28. A M6 would be a #8 so it's not much larger but it should be enough for new threads. Don't use cutting oil on Aluminum and tap it vertical for the chips to fall out. Another question would be if the socket that the screw sits in is big enough for the 1/4" -28 head to sit down in.