This is a reproduction Base 1000 DON "Dot Over Ninety" Bezel for the Omega Speedmaster, Professional and Straight-lug variants, made available by Spiralwinder Watch Parts.
If you are unsure whether this bezel will fit your Speedmaster, please contact me.

This bezel can be mounted to the straight-lug and professional Speedmaster cases. It is not compatible with the newest 3861 generation of watches. Since all Speedmaster bezels are interchangeable, this will be able to press on to the cases of all the manual wind 321 to 1861-onwards Speedies. These bezels differ from our DON bezels in that their mounting diameters have been calibrated for a firmer fit. This is so that the bezel can still fit on cases that have moderate to significant wear. For newer watches, these bezels may require slight loosening by a watchmaker. 

It has the same semi-gloss, anodized finish that a bezel from the early 60s would exhibit if new. It also has the same serifs and font as an original bezel. The steel ring is made from 316L stainless steel, and the insert is anodized aluminum — identical to the originals in composition.

To reiterate, this is not a vintage bezel — it is a modern replacement

These bezels have become very rare, and I have personally known people who have lost a bezel or accidentally dented one upon knocking their watch against something. This reproduction is meant to be a solution for those who would not like to risk the damage/loss of their vintage bezels or those who simply aren't able to justify the 10000+ USD prices of a replacement.

This has all the correct dimensions, measurements, and serifs of a vintage bezel except for some very slight alterations which have been made to ensure that this cannot be passed off as a vintage piece. Vintage 316L steel and aluminum also have inferior metallurgical compositions compared to modern steel, so it is impossible to treat this bezel as an original. 
 
To be clear, this listing is for a REPRODUCTION BASE 1000 "DOT OVER NINETY" BEZEL.