A pre-wired pair of 5.5/2.1 Plug and Socket, 5.5mm outer and 2.1mm center (5.5x2.1) the most common type.
Apart from that they are pretty standard. 20AWG, PVC double insulated wire, from the back of the strain relief to the end of the outer insulation is about 9cm, the inner wires extend about 2cm further, and are pre-stripped and tinned for you.
Don't know exactly what they would be useful for, but they looked useful.
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