Guys,
The mag I used in my mod was brand new from Wally world, and uses the hex key to get the switch out. Not the older type. I can imagine there may be some batteries out there that won't fit inside of it. If you look at the dimensions provided by the battery companies, you'll find that the normal size for a AA is 14.5 mm (.571 in). However, of all the batteries I had on hand that I measured (at least four different brands), none of them were this large, and as I recall they were all about 14mm (.551 in) or less. This makes the 4 cells put together only 1.330 inches in diameter. I don't have all the measurements I took in front of me right now (I'm at work), but I'll post them as soon as I can.