Replace the fuse or trip circuit breaker back on.
Some fixtures are mounted with a short piece of threaded pipe, called a nipple. To mount this type of fixture, screw the nipple into the center hole of the strap, and set the fixture onto the nipple. Screw a cap nut onto the nipple to hold the fixture in place.
Other light fixtures are not strap-mounted. Instead, a nipple is connected to the box stud with a reducing nut or an adapter called a "hickey." A reducing nut is threaded at one end to fit the stud and at the other end to fit the nipple. To mount a fixture that uses a reducing nut, screw the nut onto the stud and the nipple onto the nut. Set the fixture onto the nipple, set the fixture into place, and screw a cap nut onto the nipple to hold the fixture in place. To mount a fixture with a hickey, screw the hickey onto the stud, and then mount the fixture the same way.
What if the fixture you need to replace is fluorescent, not incandescent? On the next page, we'll discuss the finer points of replacing fluorescent lighting fixtures.