Use a pair of scissors to cut the old elastic.

Measure the width of the strap. In this example, the measurement was 2 cm (red line).

For the strap keeper replacement, we need to use the following formula:

Length = (Strap's width * 2.5) + 2 In our example this would be: (2 * 2.5) + 2 = 7

This means that the width of the new strap keeper would need to be 7 cm (green line).