A single small wall shelf like the one shown below consists of the shelf itself and brackets that are fastened to the wall.
The shelf is either secured to the brackets or just rests on top of them. More than two brackets are needed
for longer shelves.
1. Install the bracket with screws that are long enough to penetrate the wall stud by at least an inch or so.
2. Mark the location of the second stud.
Wall studs are usually placed 400 mm apart, so measure 400 mm from the bracket you just installed. Place a spirit level on the first bracket to extend a level line to the second stud and then hold the second bracket in position. Mark the location for the second set of mounting screws on the wall.
3. Install the second bracket with screws that are long enough to penetrate the wall stud by at least an inch or so.
4. Install the shelf on the support brackets. Use short screws to secure the shelf to the brackets.