Day-Date 40 Oyster, 40 mm, Silver Chain

The Rolex fluted bezel is a mark of distinction. Originally, the fluting of the Oyster bezel had a functional purpose: it served to screw the bezel onto the case helping to ensure the waterproofness of the watch.
It was therefore identical to the fluting on the case back, which was also screwed onto the case for waterproofness, using specific Rolex tools.
Reference 228239