This is for those who want an inexpensive replacement cable for Hifiman headphones, and can't make their own cable.
The stock silver cable that comes with Hifiman headphones tends to be very unruly. I've tried smoothing out the kinks, but the cable seems to have some sort of immortal memory of how it came in the box. And the microphonics were bad enough that I couldn't even use them sitting in front of my computer, as they made loud grinding noises when the cable slid around the desk. Searching for a shorter and more flexible replacement cable, I was dismayed to see that all cables are long and expensive, as well as commonly made of silver. I think the stock cable can be had for $60-$70, whereas most aftermarket cables are well into several hundreds of dollars. Hifiman thankfully does sell the connectors in pairs, which is probably a godsend to those who make their own cables. Points to them for selling the connectors for only $10.
But, not everyone has the skills and equipment necessary to build a cable. There's a solution.
Thanks goes to Steve Eddy for correctly identifying the connectors as SMC. Saved me the mistake of purchasing SMA connectors, which look similar, but are larger. Also agree with his comment, Hifiman probably could have picked a different connector.
SMC connectors are usually used for high speed data transmission in the GHz range. It's pretty uncommon, but there exist SMC to BNC adapters. You'll be looking for an SMC female to BNC cable. Search on ebay for "SMC BNC" and look for a short cable with SMC female on one end, and BNC on the other. There exist adapters that are SMC to BNC, but they are very expensive, and add so much length to the bottom of the headphone, that you won't be able to turn your head. I chose to go with a BNC male, as the BNC female includes a plate and threads for mounting in a panel, which adds bulk. Don't forget to order two. The SMC cable I purchased has a larger nut than the stock Hifiman connectors, but the headphones have a large enough recess to accommodate.
Next, you'll need a pair of BNC to RCA adapter plugs. They exist in all gender combinations. BNC male to RCA female and BNC female to RCA male are highly common, BNC female to RCA female not so much. A search on Amazon for "BNC RCA" will list most of them for you. I went with Gino BNC female to RCA female adapters.
The last part will be the RCA cable. There's plenty of TRS to RCA cables to be had, so you can pick whatever you like. I went with a Monoprice cable.
SMC to BNC cable 2 x $4 + $1.50
BNC to RCA adapter 2 x $4
RCA to 3.5mm cable $5
And that's the cheapest cable I could get for Hifiman headphones. The adapter stack is somewhat large, which may be a bit of a bother if you have a substantial chest. The microphonics below the adapter stack is dependent on what RCA cable you purchase. The cable is microphonic from the adapter stack and above, though that probably shouldn't be a problem except with certain collar buttons or zippers. The SMC to BNC pigtail is flexible enough that I can still turn my head 90 degrees to the left or right, though you can easily feel the weight of the adapter stack on your upper chest.
Oh, apologies to anyone vomiting at the sight of HE-500's connected to a $5 Monoprice cable. :D