couple (something) (on)to (something)
To connect or fasten two things together. We still need to couple the trailer to the truck before we can leave. I coupled the latch onto the peg, so it should stay secure.
couple something (on)to something
and couple something on (to something); couple something onto attach something to something. Couple this connector to that one. The railroad worker coupled on the next car in line. Couple the green one onto the red one.