[Tifosi]

Papajam posted an excellent description and picture a few years ago but I cannot currently find it.

This the picture you refer to?
This thread is where it came from.

 

[Tifosi]

maybe its early but i can't quite fathom how that works!?

Simpler than you might imagine:
The joint stub and reciever hole are tapered.
Baffing the side of the receiver housing very subtley distorts the receiver side of the taper which in turn pops the joint stub out.
(no permanant distortion occurs, it springs right back into shape. Well unless you've got it on an anvil and bash it with a sledge hammer)

It's kinda like popping a zit actually. Squeeze around the outside enough and all the stuff in the middle pops out.