Have you ever seen a balance that looks like a tiny helm on a ship with studs sticking out of it? That is a screw balance.
Modern mass production balance wheels are smooth, but a screw balance (often found in vintage pocket watches) has screws along the outer rim. These are regulation screws aka timing screws. Making adjustments to the screws can change the frequency that the balance wheel oscillates, therefore making adjustments to the movement’s overall rate of timekeeping.