Any clip has to be working within its ‘elastic’ range, so that it reverts to its original form having been pressed into position. This means that we are looking for a material that obeys Hooke’s Law, as shown in Figure 1. Metals such as steel have such a linear stress-strain relationship with moderate levels of stress, so would be sufficiently ‘springy’ for this application. Aluminium on the other hand, has a stress-strain graph which shows a gradual curve, and no specific yield point. You would therefore expect that to use aluminium for a retention clip would create a part which mostly springs back, but remains slightly distorted.