I have one in front of me, from my first S-3 launch. My half (other
half stays in the shuttle until the deck crew discards it) looks like
half of a palm-sized purple yo-yo. Each a/c type used a different
color as each a/c had a slightly different holdback fitting.

Agreed. And they are NOT interchangeable deliberately so Sailors don't screw
up and put the wrong one in.

If the wrong holdback fitting *could* be installed (with the associated
incorrect release pressure), the results could be disastrous. The cat could
either release without enough steam pressure to get the aircraft fully
airborne or the 'live cat' could just sit there without enough pressure to
break the holdback (instead of actually launching the aircraft) until the
steam pressure is bled off (aborting the cat shot).

What?! Are you suggesting squids occasionally eff-up?

ok, ok, I'll agree - if we CAN screw something up, at some point, some
kid will. I watched an A-3 take off once, followed by an A-7...
Problem? The cat was not reset and the Corsair was tossed off the boat
"with alacrity", causing noticible damage (belly pan detached during
the blistering fast takeoff run among other problems). Whenever
someone makes a device idiot proof, along come better idiots!

v/r
Gordon