Most shelves that use pegs have four wood or metal pegs, one under each corner of the narrow ends of the boards. The pegs insert into holes in the wall or vertical walls of the cabinet casing. The casing only needs a series of small holes to accept pegs, rather than long slots or brackets that other adjustable shelves use. Holes at regular intervals along the casing allow the shelves to be adjusted up or down, simply by moving the pegs. Pegs are also interchangeable, making insertion and replacement simple.
One drawback of shelving with pegs is that pegs can easily become lost. Replacement pegs are available at most hardware and furniture stores, and directly from shelf manufacturers. Not all pegs are alike, so you must measure the diameter of the holes in your shelving unit to select pegs that fit in the holes and secure tightly. Pegs also come with different weight ratings. For example, a metal peg that is rated for 10 pounds means that a set of four pegs can hold a combined weight of 40 pounds, including the shelf and its contents. Some pegs are round at the end that goes into the hole and L-shaped or flat on the end to provide more stability. There are even pegs with soft vinyl coatings for glass shelves and pegs equipped with locking clips to prevent shelves from accidentally coming loose.
If you plan to add shelves to a cabinet or construct your own bookcase, installing adjustable shelves with pegs is among the easiest ways to proceed. The first step involves measuring and marking the inside of the casing based on your preferred shelf heights. Next, drill holes for the pegs. Use a level to ensure that the holes are perpendicular to the vertical sides of the casing. This allows the shelf to lay flat and get support from all four pegs.
Some adjustable shelves use a series of slots or brackets in place of pegs. These shelves are somewhat more complex but may be able to hold more weight than a set of wooden, metal or plastic pegs can. Fixed shelves are another option. They eliminate the holes and grooves that adjustable shelves require, but confine your storage to specific sized items. Some book cases and cabinets include a mix of fixed and adjustable shelves to offer the benefits of both.