I've followed the theory of natural selection in settling on a profile, whatever sells the most gets reproduced more and a bit of minor random variation causes the profile to evolve. Apologies for the poor quality pic- the foreshortening obscures some of the shape, but the basic idea is still there. Concavity on both sides helps improve grip, and in general, older folk prefer the thicker ones, but not always-it's good to have a range of thicknesses. The one on the far right is prolly too thin.
As far as tips-few seem to want a small seam ripper tip paired with a large-it's redundant. A few more want the stiletto tip, but the most popular combo is either small or large ripper paired with a needle threader. For some reason, the tips are reversed in the photo-the needle threader usually goes on the narrower end for finer control. I always keep a supply of spare tips in case I'm wrong and the stiletto crowd is in town. Occasionally, people even want extra tips for even more versatility. The top request is for a cap for the ripper end which sadly I dont have
I should add that these are all longer than the tubes supplied in the kit, the extra length being necessary to get a good grip from both sides.
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