From what i know the screw holds the tension spring tight to the headlight bucket. I have a 1970 with a fiberglass nose, and fiberglass headlight buckets, and that is how mine is set up. keep in mind, mine is not a stock set-up, but a mock-up of stock in fiberglass. make sure you have the right adjusters, and the tension spring holds the headlight as it "rocks" around the opening in the headlight bucket to get your lights in adjustment. there will be tension on the adjuster spring. that is what holds the headlight lamp from flopping around. i can take some pics if you need me to.