mountable power ports

Hi, my project box is a large tin cookie box. I need to bring in +15V,
-15V, and GND lines from my external bipolar power supply. (I was
thinking I would have a separate bolt for the chassis ground, which
would go off to a big ground bus bar near my workbench.) For the three
lines from the power supply, I am wondering what would be the best (but
economical) choice for a power connector to mount into the side of the
project box. Something that sounded appealing was the spring speaker
terminal clips I see on Amazon, but the downside there is they only come
in pairs of two or four, rather than three, and they are color coded
red/black which does not quite make sense here. I am inclined to leave
the wires on the power supply itself bare on the end, rather than
attaching some specialty connector to those.

--
Christopher Howard