I don’t entirely remember where we discovered the Oxballs brand, likely from a stroll at Mr. S or a horny 2am Fort Troff shopping binge. Their designs are quite unique and I’m told much of the early products were made within the US.
One product in particular caught our kinky interest – the Sacksling “electro” edition. Our unit has a frosted silicone material sack with two removable conductive “contact” points.
These are shaped as small circles, about the diameter of small denomination currency coins. The mating connection is a female 4mm banana plug. The intention of the product is to “zap up” some pain across the scrotal area on the flat ball facing side of the metal contacts. The design is perfect for rapid deployment, as being bi-polar means no searching for another body part to complete the circuit.
After a number of test runs, we discovered a major flaw – unless your balls are making solid direct contact, the e-stim can come across as very aggressive jolts (which may be the desired outcome for some masochists) instead of more soothing electro torture. This is especially relevant in non-standing positions, where gravity may not necessarily be on your side (again, choose your own adventure when it comes to electro torture). Conductive lube is critical for this application, sweat can easily build up in the sack – we use Spectra 360 gel.
As we fancy ourselves as geeky types, we ended up adding a layer of Sugru to narrow the distance between the sack and contacting balls. 
Sugru is a rubber-cement like product, think of it as Play-doh for adults that’s designed to harden on purpose. It’s a very popular crafting tool in the maker scene, with the added benefit of being safe against body contact too! The hack is simple and effective enough to tone down the jolting.
One word of caution, the material of the sling is prone to rip easily and also doesn’t play well with other materials. We had one sling that had extreme discoloring only after a few months of infrequent use. Storing separate from other tools does appear to minimize the color changes.
