Hold the housing and tape above the plastic axle so that the axle is concentric to the hole. Pinch the middle of the spring and slide the creased end through the gap in the middle of the axle. Push the whole mechanism down into the shell of the tape measure until it is flat against the plastic.

Place the black brake button into the bottom of the shell before closing it.

If creased end of spring is not put into the gap in the axle, then the spring will not be able to reel in the tape.