As detonation occurs, the diaphragm
strikes the inner pin once causing it to
rise and close the contact points.When
the pin drops back down there are no
contacts for that detonation because the
inner pin shoulder keeps it from touching
the diaphragm and bouncing upward
again. An Alnico magnet is used at the top
of the inner pin so that when the contact
points close they are held together 
magnetically until the inner pin starts to
descend. The upper contact points
break apart quickly and cleanly.

At right: Micrometer Head Bouncing Pin:
 
 
 

Many designs included a micrometer
adjusted inner pin so that only one contact
per detonation would occur if the 
micrometer head was propery adjusted.
These became known as " micrometer
head bouncing pins".