SlugLife
Contributor
In the US, most of the ones shipping from china end up being about $7.First known as "fixe-palmes" ("fin fixers"), these three-way straps were patented by Paul Beuchat of French diving equipment manufacturer Beuchat back in 1960. The patent is reproduced below in the original French and in a rough English translation I made:
Two Beuchat advertisements. The first is dated 1959, revealing that the device was on sale a year before the publication of the patent. The second from 1961 illustrates the fixe-palmes in action in choppy waters, maintaining closed-heel fins on feet.
Now known as fin grips, fin retainers and fin keepers, they come in various sizes and are available in a spectrum of colours designed to contrast with fin colour in Japan, where the following were made by diving equipment manufacturer Ikari:
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The following silicone examples are currently available at approximately $5.99 post-free on eBay:
Here's the scuba-choice version, about $9 (they also have red and yellow). They don't have a size-chart, but from what I've seen, US-men-9 is medium, and US-11 is large. ScubaChoice tends to be similar to the unbranded products from china, but their products seem to always be of reasonable quality. Cresi has them as well, for about $9 and good review. IST has them for around $10