A Short Glossary of Parts Found in an Automatic Watch

When reading about watches, you will hear a lot of part names thrown around. Below is a list of some of the most common parts of an automatic watch and a brief description of the function of the more common (or interesting) bits.

1. Crown Wheel: the crown wheel engages with the winding pinion, which is sits on the stem, which is attached to the crown, which is the little knob on the side of the watch that you pull out to wind the watch or set the time. When you turn the crown, the stem rotates the winding pinion which in turn rotates the crown wheel, which engages with the…

2. Intermediate Wheel: not all automatic watches have an intermediate wheel, but they sometimes used in conjunction with the…

3. Auxiliary Wheel (Wig Wag): the auxiliary is not an essential component, but it does offer a useful benefit in automatic watches. The auxiliary wheel, or ‘wig wag’ wheel, has a floating axis enabling the rotor or oscillating weight to be disengaged in the act of winding.

4. Ratchet Wheel: the ratchet wheel sits on top of the barrel, which contains the mainspring and when it is turned, the mainspring is wound around the post in the barrel, which we call the barrel arbour.

The following parts are rare and their functions might be confusing at this stage, so I will skip straight on to describing the more run-of-the-mill components.

5. Ratchet Driving Wheel Pinion
6. 3 Arm Spring
7. Ratchet Driving Wheel
8. Reduction Wheel & pinion
9. Winding Wheel & Pinion
10. Stop Pawl
11. Stop Pawl Spring

12 & 13 Reversers: reversers are really what make a bi-directional weight work so well. The reversers, thanks to a series of internal brakes and springs, take the rotation of the weight, no matter which direction it is turning, and convert it into ONE direction, so the mainspring can be wound constantly. This is essential. Without the reversers, bi-directional winding would be impossible as the mainspring can only be wound in one direction, around the barrel arbour (rotating it in the opposite direction would UNWIND it).

Another couple of rare ones:
14. Mobile Platform
15. Intermediate Pinion

16. Pinion attached to Oscillating Weight: this pinion engages with the reverses, or the intermediate pinion if that separates them, and transfers the movement of the weight to them.

17. Oscillating Weight: the usually semi-circular weight that winds the watch by way of the wearer’s movement. It is also called a rotor weight, or just a rotor.

18. Winding Stem: the bit attached to the crown that is pulled into different positions when you wind or set the watch. The winding and sliding pinions both sit on the stem and are moved into different locations in order to perform different functions with every position of the crown.

19. Winding Pinion: here we are, back to the beginning again! The winding pinion sits on the stem and engages with the crown wheel so that the watch can be WOUND.

If you have heard of any other parts that you would like an explanation of, or would like further information on any of the above parts, please comment below and I will respond as quickly as I can.

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