Just a few inputs on the "Naiad" term and crowns (Naïad = Greek nymphs living in Water
)
Omega used the term first in 1937 on a watch called the Naïad. The first "standard" waterproof watch after the Marines watches. With a waterproof snapback case! and the first crown using a internal gaskets that sealed against the stem tube.
This was then refined on the first gen SM300 watches. The 2913 came with a crown system that was named Naïad. Still using internal gaskets that sealed against the stem tube, but a more advanced design where the seal went tighter the more pressure it got (see catalog picture below fra "old-omega.com"). These crowns were used also on the 2. gen SM300 (165.024) until Omega introduced the screw-down crown on these in the late 60'ies. The Mercedes mark was found on some late 50'ies crowns, both on 2913, -14 og -15 and some others. The mark has NOTHING to do with the Naïad system or name. This is a common misunderstanding. It's is just believed to be a sub-manufactorer mark. Below is my 2913 Mercedes crown pictured. Remember that the SM300 crowns are a bit smaller than the speedmaster ones. Almost same diameter, but the deepth is shorter. And of course the stem size is different. Tap 0,9 on the SM300, on the speedy 1,0 and on the railmaster 1,2
The flat feet crown posted above is the original one found on both 1 and 2. gen SM300 upto late 60'ies. The OP's one is the replacement crown.
On a side note regarding the waterproof issues with the Naïad sm300 crowns. You can read most places, that the reason why Omega introduced the screw down crown was because the Naïad crown had a design fault, where it leaked water at shallow deepth because of not enough pressure to make the seal system work. This is actually not correct, it was because the gaskets wasn't replaced/serviced in time/got old and stiff on many watches, not because of the system. So it was more because of customer perception and the fact that Rolex subs had screw down, that Omega shifted to the screw down.
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