Guaranteeing the external distance from the rebar to the formwork (usually 1” or 25mm) and also the spreading between the bars (internal distance). It's usual to see this kind of rebar configuration in containment walls and prefabricated construction elements such as concrete pipes.

​

These spacers come in a variety of internal lengths, down to 100mm up to 200mm and can take mesh as thin as 3mm and rebar up to 1/4”.