Even more preferably, the cross-sectional dimension Z of the knuckle portion 61 is in the range between and including about 2 to 2.5 times greater than the cross-section dimension F of the finger portion 65, with typical dimensions comprising the ratios of 2.5 mm to 1.25 mm (2 times) and 2.5 mm to 1 mm (2.5 times).