IMPULSE PIN/ROLLER PIN

It is an elliptically shaped ruby pin (synthetic corundum) that is friction-fitted or glued into the roller table, which is itself friction-fitted onto the balance staff. 
The impulse pin interacts with the pallets of the lever. It unlocks the lever via the pallet it’s attached to and receives its impulses in return.

Useful links:

• – Lever
• – Balance wheel
• – Escapement adjusting