These are one-touch connection connectors that allow you to connect cables simply by inserting the stripped wire while pressing the button. No soldering or tools are required, and they can be attached and detached repeatedly. They seem to be sold on Amazon and Mercari for around 360 yen for two. I have no use for them, so I'm offering them at a super special price of 50 yen each. The compatible wire thickness is up to AWG18 / 1.0mm / 0.75SQ. The cable fits perfectly when the insulation is stripped 8mm. The fourth image is a combination with the RCA female connector also on sale. If you purchase the items also on sale at the same time, I will discount the shipping difference, so please feel free to contact me.