The Early Rolex Oyster Screw Down Crown

[David.Boettcher]

I have just had an article on early screw down crowns, including the Rolex screw down crown, published by the NAWCC in the December Watch and Clock Bulletin. I thought a short synopsis of the Rolex part might be of interest here for those who don't receive the NAWCC magazine.

The Rolex Screw Down Crown

Some 30 years after screw down crowns had been invented in America and applied to pocket watches, but didn't find a great demand, the increasing fashion for strapping a watch to the wrist meant that better sealing became an urgent necessity. However, the American designs appear to have been either unknown or forgotten in Europe, and had to be invented all over again. Hans Wilsdorf, Managing Director of Rolex and an early proponent of wrist watches, was on the alert for designs that could achieve this.

In early Rolex Oysters, the number 114948 is usually stamped inside the case back. This refers to a Swiss patent registered by Paul Perregaux and Georges Perret of La Chaux-de-Fonds on October 30, 1925, and published on May 17, 1926. Wilsdorf must have thought that this was the breakthrough he had been looking for, because he bought the rights to the patent, and then registered it in Britain as GB 260554, and also in Germany and the United States.



The winding stem 4 and socket 6 are screwed together to form a single item. The crown 8 is connected to this stem and socket assembly by two screws 9 and 10. The ends of these screws slide in the yellow longitudinal slots 11 and 12 in the socket. This permits the crown to move axially with respect to the stem, as shown in the difference between figures 1 and 2, whilst being locked to the stem rotationally. As the crown is unscrewed from the case, the two screws slide up the longitudinal slots until the crown is clear of the pendant.

The screw threads on the pendant and inside the crown are left-handed, for the same reason as in the Fitch patent. When the watch needs winding, the crown is unscrewed clockwise, in the direction of winding. Once the watch is fully wound the crown is screwed back down anticlockwise, against the mainspring winding ratchet. This has the same drawback as the Fitch patent, in that the crown can then not be unscrewed again until the watch has run down.

Another poor feature of this patent is that the waterproof seal is formed by the gasket 16 against the case, which is in a very exposed position, and would not have lasted long given the gasket materials available in the 1920s; leather, cork or felt.

Because of the left handed thread and the problems in winding and hand setting, and the clumsy gasket, patent CH 114948 wasn't suitable to enter production. Wilsdorf got the technicians at Aegler working and by October 1926 they had come up with a much better design. The patent for this was registered on October 18, 1926 as Swiss patent CH 120848.



This design incorporates a clutch which makes it a much more usable design. A dog clutch is formed by the yellow square 12 formed on the stem engaging/disengaging with the red square hole 9 in the base of socket 6. When the crown is screwed down on the pendant the yellow square is free of the red hole as shown to the left, and the crown can turn freely without turning the stem. But when the crown is unscrewed from the pendant, as shown on the right, the yellow square engages with the red hole, and turning the crown then also turns the stem.

The seal is also better than the Perregaux and Perret design. Although it is not discussed in the patent, the seal is formed between the shoulder on socket 6 and the end of the stem, and Rolex used a lead gasket here to get a better seal without using organic gasket materials.

The CH 120848 Mystery

Curiously, patent CH 120848 isn't mentioned in Oyster case backs, and I have not been able to trace versions of it being registered in any other country. I am a bit mystified about this, as CH 114948 / GB 260554 was also registered in many other countries, and appear in every early Oyster I have looked at, whilst having very little to do with the actual production design, whereas the much more significant 120848 doesn't get a mention. Maybe Wilsdorf didn't want to spend any more money on overseas patent registrations for CH 120848 and decided to rely on the protection afforded by the multiple registrations of CH 114948.

Regards - David