Need help understanding terminal cups
 

Its been bothering me for some time now, When building your own box one would use terminal cups. Now say your running 4ga wire to them Whould you just get a 4ga spade terminal and screw it into its corresponding pin? Also on the other side of the cup (* the one in your box *) what ga wire should you use? after google'ing it i found some pictures and it looks like the person was useing 12ga(ish) wire. it just seems weird After useing such big wire to downgrade to the small wire.

Any thoughts?

use the same size on both ends, though most people i know dont use cups they just drill a hole for the wire to go through then seal it up from inside.