Inside the case back and enclosed in a triangle is the Omega logo Ω and the wording OMEGA WATCH Co - the last 'o' in WATCH Co is always smaller in size than the rest of the type. Copy below the triangle reads FAB. SUISSE and SWISS MADE.
ACIER STAYBRITE is the trade name for steel used by by Huguenin Frères. The Staybrite brand was created in 1954and belonged to Firth Stahl Verkaufs SA company a company owned by Firth Brown Group. It was subsequently purchased by British Steel who sold the business in 1979 to F.W. Hempel & Co the current owner of the mark.
Staybrite 1.4301 steel used by the watch industry at the time was composed of 18% chromium and 12% nickel, which is close to 316 L steel (16-18% chromium and 10,5-13% nickel) the industry standard at the time.
Below the case manufacturer's HF logo follows the case reference and in the case backs illustrated above a dash and then the year of production. The year of production does not appear in all case backs.
The first three numbers of the case ref 165.024 comes from the following Omega table.
1 = Gent's watch. 6 = Automatic winding centre seconds. 5 = Water-resistant. The 024 is the model number for the SM300.
1 figure 2nd digit 3rd digit1 - Gent's watch 1 - Manual winding without seconds 1 - Non water-resistant 2 - Gent's jewellery watch 2 - Manual winding small seconds 2 - Non water-resistant date 3 - Gent's bracelet watch 3 - Manual winding centre seconds 3 - Non water-resistant chronometer 4 - Gent's jewellery bracelet watch 4 - Manual winding chronograph 4 - Non water-resistant chronometer date 5 - Lady's watch 5 - Automatic winding without seconds 5 - Water-resistant 6 - Lady's jewellery watch 6 - Automatic winding centre seconds 6 - Water-resistant date 7 - Lady's bracelet watch 7 - Automatic winding chronograph 7 - Water-resistant chronometer 8 - Lady's jewellery bracelet watch 8 - Electronic chronograph 8 - Water-resistant chronometer date 9 - Electronic
The date version is numbered 166.024.
There are many theories regarding the reference S.C. One is that it is just an abbreviation of Steel Case. Another is that it stands for Seconde Centrale (centre seconds) but as can be seen in Pic 6 the S.C. was dropped at some point. Note also that the case ref.165024 does not at this stage have a full point in the middle.
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Pic 7 shows the inside a Centrale Boîtes S.A. case back. INOXYDABLE, which means stainless, has now replaced the word STAYBRITE. This indicates a change in the steel supplier for the cases. Pic 7 also shows that at some time during production a full point was introduced into the model number ie. 165.024. Many cases also had the date after the model number as can be seen in Pic 6.
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The wording and logos on the outside of the case back Pic 8 remained the same throughout the production of the SM300.PIC.8
Pic 9 illustrates that the very early cases (bottom pic) had a slightly different profile around the outer edge and case opening slots.
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Ω Crowns.
The Naiad non screw crown (1962 to late '67 or early '68) is 3.15mm deep and 6.7mm in diameter with 24 grooves.
The screw down crown (late '67 or early '68 to end of production) is 5mm deep and 6.2mm in diameter with 22 grooves.
Pic 10 and Pic 11 show original Naiad crowns.
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The Military issue SM300 was introduced in 1967 and part of the specification for the Military watch was a screw down crown.
The change of crown for non-military watches probably came about as a result of this so that the production of only one type of case was required. Pic 12 shows a screw down crown.
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Ω Crystals.
Omega describe the crystal as 'domed triple layer Hesalite'. My understanding is that Hesalite is Polymethyl Methacrylate (plexiglas). The domed crystal stands proud of the bezel by about 3mm and is engraved in the centre with the Omega Ω logo.
Ω Serial numbers.
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Each Omega movement has its own unique 8 digit serial number and the table below correlates numbers with date of production. Although the table is not 100% accurate it is a pretty good guide. Only the years of production of the 165(6).024 are listed.