Sliding gear, mounted!

Looking through the parts bin for yet another elusive component I was sure I had I came across this work of art :-)
Smaller than a fingernail.
Not my favourite name for a part though - that's reserved for the 'wig-wag pinion' :-)
The watch it's sitting on is a 1974 Breitling Navitimer powered by a Calibre 12 movement which uses this very component hidden deep inside.
The movement itself is basically an upgraded Calibre 11 used by the Steve McQueen Heuer Monaco introduced in 1969.