The metal tip of your tape measure fits into the slot on top of the Speed Rocker allowing you to hold both and eliminating the need for a third hand. This also positions your thumb directly over the blade to give you maximum pressure for scoring a line. To change blades simply pull up on the black clip on the top of the Speed Rocker and pull the blade out the front. To re-install a blade, simply slide the blade in the front blade slot and snap the black clip back into place. The blade can be fixed in any of three positions. This is a non-retractable blade so store this tool carefully away from children or remove blade at the end of use and store in the handle. Two utility blades are included. Uses standard double-end utility blades. Made in China.