I'm not to certain I go to the local hospital supply store, and buy surgical tubing. I then double it over, and slide a key ring on in. Actually thats backwards I slide a keyring on it, and then double it over. Tension varies by model wight but it needs to be pretty strong. About 20 feet long, and the ring hooks to a dowel that sticks up from the base of the launcher through the hole in the front of the pedal. Then run a heavy stringer from the ring to the hook on the model. A couple of strands of heavy duty nylon cord work well, Or you could use some heavy duty steel fishing leader wire.
The bungee hook typically should be halfway between the nose, and the CG. You don't want it too far back or the model will pitch up on launch. Make sure the bungee hook is very secure because unlike a glider high start bungee launchers for jets are shorter, and really snatch them. Seems everybody uses a different amount of tension. A fishing scale makes a good way to check the weigh of the bungee's pull.
A 5 lb model typically needs about 15 lbs of thrust. Also be sure to do some trim flights before you bungee launch!
If it's out of trim, and you step on the pedal it's going 0-60+mph.
Find a hill, and install nothing but a receiver, and a small receiver battery pack, and of course your servos. Make sure the CG is good to go, and gove it a god handlaunch off the hill. That way you can get it trimmed up, and make sure nothing is severel out of trim.
Bungee launchers are not forgiving on fresh jets. I don't know how many stories I've heard on the E-zone of someone putting a new EDF on a bungee launcher for the first flight, and going home with scrap parts.
Also hit the throttle untill it leaves the bungee. I hope that helps, and sorry if it's a little mixed up. I just woke up, and am having my coffee.