/diy/ - Do It Yourself

>>1622336
I got a Soviet Tankist helmet that I want to make an adapter to 3.5mm AUX jack.
The pins for the speaker are the two that are far apart. Each pin is about 2.5mm diameter, 10mm high. My question is, which of the usual hobby/RC connectors would be a good fit?

I couldn't find any resources on the dimensions (inner diameter) of usual bullet connectors (EC3, EC5, XT60, HXT...etc.). A video suggests using EC3 with a bit of crimping, but I'm curious to know if there are any other alternatives.

On a somewhat related note, any suggestions for a decent multimeter?

>>1610638
I'm trying to make an adapter for a Soviet Tankist helmet, but I'm finding difficulty with the wiring.
The two plugs far apart from each other are for the speakers, while the closer ones are for the laryngophone. I'm going to use an EC5 that is slightly crimped for a snug fit, and I'll solder wires to them as this guy has already made: https://www.youtube.com/watch?v=GWxKplY0vu8

However, when looking at a TRS connector, it apparently requires a "ground" wire as well, which is not included: https://www.youtube.com/watch?v=PZcifo0XQA0
How is it possible to get away without a "ground" connection? I thought it was a necessary component. What are the dangers in lacking it?