Can anyone tell me the correct thread size for the bolts that connect to the side terminals of a battery? I've tried 3/8 x 16 but it seems loose.

I use an 8mm socket or wrench to loosen up the bolt that connects cable to terminal.Its a little nut and its a little tight in my 91 space wise but it works fine.

Thanks for the reply, but I'm looking for the thread size.

my bad went to work for 815this morning only 4 hours of sleep still up sorry again

I always just use "OEM bolts" from Wal-mart or Advance Auto Parts to replace any rusted side-terminal bolts (like two bucks for two of them).

The reason I'm changing them is because I'm adding extra wires with lug connectors directly to the battery and I'm running out of thread to go into the battery. I found some extra long battery bolts at auto zone, but these are too long. I would just cut them but they aren't threaded all the way. I tried threading them the rest of the way with a 3/8X16 die but the're slightly thinner in diameter on the smooth part and there isn't enough meat on them to get a good thread.
I may try to use a regular bolt that's just the right length so it doesn't bottom out, with a couple of washers and see if I get a good connection. Thanks for the reply.

Most hardware stores have thread "cards" in the bolt isle. It has all diff sizes of nuts and bolts imbedded in the card w/their sizes - you thread your bolt into the nut it fits a viola - now you know what the size is. Very handy. If not you can always add a few washers.