Your meaning is not clear. - If you are going to tap the threads in, use a 7/32 drill bit. If you want a hole that this bolt will slip through, use a 9/32 drill bit.
For a 3/8 bolt, you should use a 5/16 drill bit.
For a 3/8 bolt, you should use a 3/8 drill bit.
For a 1/4 bolt, you should use a drill bit that is slightly smaller in diameter than the bolt itself. In this case, a 7/32 drill bit would be a good choice for drilling a hole for a 1/4 bolt.
For a 1/2 inch lag bolt, you should use a drill bit that is slightly smaller in diameter, typically a 7/16 inch drill bit. This allows for a snug fit and proper anchoring of the bolt.
Motor oil in small amounts
drill 2 holes at each end of the bootlid to correspond to the threaded bolts on the spoiler then sit the spoiler in the holes and bolt from inside.
Well your gonna have to have a new mount bolt. Drill it out so that the drill bit is the same size as the hole the bolt goes into. Snap the head off when you drill past thehead. The bolt should hand screw out. If not use vicegrips. Then put the new one in the same place. Should replace the mount aswell.
For installing heavy-duty shelves in your garage, you should use a 3/8 inch lag bolt drill bit.
There should be a stud (not a bolt) threaded in to the head and the stud should have a thread sealant applied to the threads.
Cut the bolt head off with a cutting wheel then use a drill to drill out the bolt.
Cap screw
To accommodate a 3/8 bolt, drill a hole that is 3/8 inch in diameter.