This was originally for 2X20 lamps but I converted it (temporarily) to slimline. I converted this just to test the ballast and lamps. I actually have a fixture arriving in the mail that these lamps and ballast will be going in. It’s a Day-Bright strip with reversible lamp holder brackets. The lamp holder brackets that are in this Lithonia strip are from my Lithonia 8 foot strip, which just so happens they fit in this fixture!