Earlier, jcarlyle wrote:

...what's a pip pin?

Generally, it's a mechanical pin retained by one or more balls at the
tip that protrude beyond the cylindrical body of the pin. The balls are
either spring loaded, or are allowed to retract when you press the
button on the handle of the pin.

Here's a picture of a typical locking pin:

http://www.aircraftspruce.com/catalo.../qkrelease.jpg

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24