I just installed one of these in a circular fluorescent light fixture having an inner 12" (32 watt) circline tube and a 16" (40 watt) circline tube. This ballast had slightly different dimensions that the oddball Chinese ballast that was originally in the fixture, so I had to drill two new holes and use self tapping sheet metal screws to secure the ballast to the fixture. Took less time to do that than to explain it here. It would be nice if Keystone would provide a couple of self tapping sheet metal screws and a brief set of instructions on how to do that along with the ballast. It is pretty self evident what you need to do, but it would still be nice. After installation, I flipped the breaker on and the the light switch on and both tubes fired right up. Nice and bright. I did try to find ballasts like this at the local lumber yards and do it yourself stores, but they didn't carry these. Am very glad that Amazon does. Just ordered another one to keep as a spare.