Incabloc shock protection system
The Incabloc shock protection system is used in mechanical watches, to protect the critical alignment of components in the event of an unexpected physical shock, such as being dropped onto a carpeted floor.
The pivots and jewels of the balance are fragile in comparison to the mass they need to support, and without shock protection are the most likely part of the watch to be damaged under impact.
The Incabloc system uses a special shaped spring to allow the delicate jewels and pivots to shift in their settings under impact until a stronger shoulder of the staff contacts the strong metal endpiece. When the impact is over, the springs guide the parts back to their original positions.
Similar systems are ETA's Etachoc, Rolex's Kif, Seiko's Diashock, and Citizen's Parashock.