Case Dimensions: The case width of the 1675 comes in at 39 mm in diameter, 2 mm wider than the 6542 case. From 1959 to 1967 there were so-called ‘thin cases,’ which maintained the thickness of the 6542 and were approximately 12.7 mm thick from case back to plexi. After 1967 the case thickness increased to 13.0 mm and was maintained until the end of the production run. The case length from lug to lug is 47.5 mm. Source
Crown: Crowns on the 1675 were Rolex ‘twinlocks,’ 5.3 mm in diameter, and featured the Rolex coronet with an underline underneath. The twinlock crown system has two rubber gaskets. One gasket is inside the crown and compresses against the threaded tube attached to the watch case. The other rubber gasket is located inside the watch tube and encompasses the winding stem. Together, they prevent water and dust from entering the case. While the gasket in the watch tube can prevent water and dust from entering the movement even while the crown is unscrewed, don’t be an idiot – screw down your crown. Source
Crown Guards: Crown guards are found on all 1675’s. Early models, from 1959 to 1964 (seen as late as SN 113xxxx) featured the pointed crown guard, also referred to as El Cornino or ‘the horn.’ The Type A and B non-chapter ring gilt dials always are cased with PCG’s; early Type C dials are also seen with PCG’s up to the SN noted above. The crown guards were upgraded to the shaped/rounded crown guards seen from 1964 onwards. This area is prone to polishing and should be checked carefully to assess the condition of the case as well as refinishing.
Crystal: The standard crystal for the 1675 is not in fact a crystal but a plastic acrylic “plexi” designated Tropic 116, which was fitted with a so-called ‘cyclops’ window over the date wheel for magnification. Aftermarket crystals often lack the magnification of OEM plexi’s and do not fit flush. Service crystals have a larger bevel on the edge. A non-cyclops option, the Tropic 38, was also available for the 1675 and is sought after – see the pictures below. Source
Unpolished Lugs: the first example (pictures 1-4) is worn but honest and the second is barely worn (pictures 4-8). Note the similarities in the shape of the lug and the distance from the lug hole to the edge of the chamfer. Examples from the early 60’s have accentuated bevels (picture 9) compared to the later matte dials, which generally have the same bevel width from lug to lug.
Unpolished Crown Guards and Crown: on the rounded crown guard case, note the facet between the top of the case and the rounded edge, this is often the first thing to be lost in polishing (but can also be lost with a lot of honest wear).