[rheavn]

Just used this tool the other day on two basement doors.  I've made several & used to give them away at Guru rallies.

http://newellgurus.com/showthread.php?tid=48     Pictures & specs are here.

Tip:  Unscrew the old gas spring from the rear ball socket end.  Then screw the new gas spring into the old ball socket.  Now you just have the front ball socket to hook up.