Measuring tapes usually come in a case or a roll. Blades for housing-style tapes consist of steel, fiberglass or cloth. Many are for measuring linear distances, and cloth tapes work for measuring circumference as well. Several encased measuring tapes have a spring-loaded mechanism so you can retract them automatically by pushing a button. Most steel and fiberglass blades have a locking mechanism as you extend them so that you can take measurements with one hand. A clip on the end of the blade grasps onto the material. Encased cloth tapes sometimes have a slot in the housing so you can manually lock the tape when measuring circumferences. Cloth and paper roll tape measures have the give necessary for measuring circumferences. Some have a double-sided adhesive on the underside of the blade to you can affix them as a permanent measuring device on surfaces like drawing boards and work benches.