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Grab a bag of the metal shelving clips I've attached a photo of (Home Depot or Lowes) Don't bother with the plastic push-in clips the installer used. They are junk. If you're going into a stud, simply use the screws from the package. You won't be using the plastic wall anchors. It doesn't matter if you have metal or wood studs, as the screws work fine in either. There is no need to pre-drill.

If you are placing them where there is no stud, pre-drill a 1/4" hole, and insert two wall anchors.

Regarding what type of wall studs your home has, wood or metal (your home might have both), the easiest way to find out which you are dealing with, is to use the magnets I've attached a photo of (available from Amazon). I use them all the time, and there is absolutely no need to pre-drill holes, open up the wall, etc, to find out what type of studs you have. The magnets are quick and easy to use. When it finds a stud which is wood, you'll be able to tell, as its attaching itself only to the drywall screw locations. If it's a metal stud, the magnet will attach the entire vertical length of the stud.

Hope this helps.