In the picture below the catapult hold-back is being attached to this VA-153 Skyhawk just prior to tensioning the "cat". Note that the hold-back is not quite yet totally slid into the slot on the hol-back 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 catapult 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.