For anyone removing/replacing the power window motor looking for the correct size fastener and length, no one seems to recommend specifics other than "get some bolts that fit". Here's what I used, should save folks the frustration what to get when at the hardware store.
Quantity 4 each of: 1/4-20 button head 5/8" long bolts / screws, washers, lock washers and nuts. Button head should be on the inside, it is shallow enough to clear any items that move inside the door.