Origins of the 3646 case construction


Most books about Vintage Panerai show a very isolated view on the references which were delivered by Rolex to Panerai. By putting Panerai into the historical context and including further data, also from movement suppliers such as Montilier, Cortebert and Angelus we can get a much more comprehensive view on these fascinating watches.

Connoisseurs of Vintage Panerai are aware of the Rolex markings on the cases. Rolex was already offering Ref. 2533 in 1935 and Panerai could have received ready-made watches. What was Panerai’s contribution to the development of the cases, besides the sandwich dials?

Richemont Panerai doesn’t mention the unique cooperation between Rolex and Panerai in their timeline and markets the watches as “Italian Design”. On they say: 

“On the eve of the Second World War, Panerai creates the first prototypes of the model now known as “Radiomir” for the frogman commandos of the First Submarine Group Command of the Royal Italian Navy.“

> Richemont Panerai history

Pictured is a watch with “California” dial. This dial was invented and even patented by Rolex and the watches were delivered with those very dials to Panerai.

Early Panerai with “California” dial on


>The Complete History Of the “California Dial”


Multi-part case construction of Ref. 2533/3646

The case construction of Ref. 2533/3646 consists of several parts. The movement is carried in a movement retaining ring with external threads. This ensemble sits in the middle case. Bezel and case back are screwed onto the external threads of the movement retaining ring, rotating in opposite directions and clamping the middlecase between them in order to form in combination with lead seals a hermetically sealed body.

Case construction Ref. 2533, Panerai – Una storia Italiana


François Borgel

Above case construction probably goes back to a patent from 1903 when François Borgel, a case manufaturer from Geneva, filled a patent for a hermetically sealed 3-piece case.


New Borgel Screw Case
Borgel 3-piece construction 1903 ( © David Boettcher)


“This new hermetic screw case is formed of three pieces; the bezel, the bottom and the middle case, all three are screwed on the movement retaining  ring in which is fitted the movement. These closures are hermetically sealed and the case is very strong.”


Borgel already had a patent from 1891 for a hermetically (impermeable) sealed 2-piece case.

Borgel 2-piece construction 1891 ( © David Boettcher)


The crown was not screwed down. A spring would retain it against the pendant (collar of the case). This construction was primarily a protection against steam and dust.

> The history of the Borgel watch by David Boettcher

> The History Of Dive Watches


Rolex Oyster

It is more than conceivable that Borgel’s case construction inspired Rolex in the development of the first Oyster case by the end of 1926. The construction is almost identical. The design of the waterproof Oyster case was patented in 1926 (CH 120851).

Hans Wilsdorf bought the patent for the screwed down crown (CH 114948) of Perregaux et Perret in July 1926 and improved the system with a clutch in order to disengage the crown from the stem while being screwed down (CH 120848).

Case construction Rolex Oyster case 1927


This is the same construction like Ref. 2533/3646. Rolex produced different Oyster versions in the late 1920’s and 1930’s using this case construction. There is also one with a cushion design.

Early Rolex Oyster with typical cushion design


There are indications that C.R. Spillman SA in La-Chaux-de-Fonds produced the first Oyster cases for Rolex. C.R. Spillman was also involved in the transfer of the screw down patent CH 114948 from Perregaux et Perret to Hans Wilsdorf.

> The history of the Oyster case by David Boettcher



It becomes pretty obvious that Panerai did not have much involvement in the development of Ref. 2533/3646 cases. Panerai’s contribution to these watches were the ingenious and beautiful plastic dials with rivets and later the even more sophisticated sandwich dials with three different layers where the dangerous radium luminous material was safely contained in cells. 

In interviews Mr. Angelo Bonati (CEO Richemont Panerai) insists that the design was strictly italian, even that Giuseppe Panerai himself designed the 3646 and Rolex only supplied the movements.

> Interview: Angelo Bonati for Panerai

Early 2533 with typical Oyster case back bearing international patent numbers

Great Britain Patents

260554: Screw down crown (Rolex, Ex Perregaux et Perret)
274788: Improved screw down crown (Rolex)
274789: Oyster case (Rolex)

Swiss Patents

114948: Screw down crown (Rolex, Ex Perregaux et Perret)
120848: Improved screw down crown (Rolex)
120851: Oyster case (Rolex)
122110: Alternative screw down crown (Rolex, Ex Philippe Weiss)

USA Patent

1661239: Screw down crown (Rolex, Ex Perregaux et Perret)

German Patent (D.R.P. = Deutsches Reichspatent)

443386: Screw down crown (Rolex, Ex Perregaux et Perret)
471002: Oyster case (Rolex)


Case back 3646 Type D


Italian vs. Swiss design

Panerai developed their first own prototype “Prototipo Uno” around 1950. It was based on Ref. 3646 using the same parts but with a different middle case. The lugs were reinforced and made from the same block of steel.

Italian design developed by Panerai

In my opinion this is how the “real” italian design looked like. The shape is inspired by instruments such as depth gauges and compasses made by Panerai. A very similar design was also used for the first watch completely developed by Panerai, the GPF 2/56 with Angelus 240 movement.


Photo credits: Vintage Watch Straps, Juwelier Wagner, Panerai – Una storia Italiana


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