"Robert11" wrote in message
. ..
Hello:

Retired Engineer.

Have always been interested in carrier catapaults.

I have tried to find a good, relatively technical, description on the web
with some diagrams or pix of the aircraft hold-back mechanism that's used
immediately prior to launch that restrains the plane.

Doubt that they still use breakable (frangible) type of bolts, but perhaps
?
Do they ?

The 'breakable' holdback certainly is still in use today. It's not a bolt,
but looks more like a 'double mushroom' where the center has been machined
down to certain specs. It is designed to separate at a predetermined stress
point.