In the picture below the catapult holdback is being attached to this VA-153 Skyhawk just prior to tensioning the "cat". Note that the holdback is not quite yet totally slid into the slot on the holdback unit on the Skyhawk. The "breakaway link"
(just left of the crewman's right hand finger) will break at a predetermined strain and release the Skyhawk as the catapult shuttle fires. The straps are to keep the cable from rebounding and slappping around.
On the deck in the background is a spare "bridle", the cable used from the catpult shuttle to the aircraft.
"According to NAVAIR Lakehurst "For the A-4 "Skyhawk" the holdback bar PN was 609329-1 and the "tension bar" was PN 502822-4. The tension bar was painted yellow and blue and had a breaking point of 28,500 +/-1,500 lbs."
This information is in Document NO. O-12 "AIRCRAFT LAUNCHING BULLETIN for ALL STEAM CATAPULTS AIRCRAFT LAUNCHING ACCESSORIES". Doug Cooper.