I guess it's understandable that there are lots of models that were uncatalogued from this period. They may have been used for export markets other than the US.
One such model is a Thinline example that is known only by the number on the back... 912373. Generally speaking, the serial number of cases is irrelevant. It mattered only to the maker of the case. However, in the 1960's two sets of numbers started to get added to cases. One was the unique serial number of the watch case, and the other is a number that indicates the model that the case was used for. Most of the time the watch had a model name but sometimes all you have to go with is the model number. Typically the last two digits of the number represents the year the watch was introduced. When there's a dash at the end, the number after the dash represents the case material.
Anyway, I recently landed a Thinline project watch and at first blush I thought for sure I'd be able to identify it.
The 12, 3, 6 and 9 hour markers have a black stripe, which I thought would be a good clue. However, the best I could come up with was a 1968 Thinline 6505. There are some key differences though. For example, the hands are luminous and the other hour markers are about as long as the 12, 3, 6 and 9. Close but no cigar.
When I looked at the back I saw several interesting tidbits. First, there are a few scratches from someone trying to open the case. Stainless steel backs on yellow cases always tempts the uninitiated to try to remove the stainless back. Also, the model number is stamped there, making it clear this is a 1973 model. Lastly, the case material has a "base metal bezel". That's very unusual in pre-1969 models... pretty much unheard of for vintage Hamiltons, in fact.
Removing the crystal gives access to the dial. Positioning the two piece stem allows the movement to fall out the front of the case. The radial-finished dial looks great. No moisture appears to have gotten into this watch.
Inside is a Hamilton 639 movement based on a Buren grade. This is a classic Thinline movement and appears to be untouched since it was first installed.
The inside of the case back is properly stamped, so it's a legitimate Hamilton model. The serial number inside is unique to this watch.
It's nice to work on a manual-winding watch for a change. I feel like most of the watches I've done as of late have been very challenging micro-rotors. This is a nice break. Everything is cleaned and dried.
The reassembled movement is ticking away nicely. Now it's off to the timer to see how well it's performing.
Not too bad. On most watches all I would do is slow it down a smidgen but this caliber is easy to adjust so I will try to dial it in more precisely.
A tweak here, a tweak there, another tweak to correct the other tweak... eventually I get everything to line up where I want it. It doesn't get any better than this.
Thinline models with sub second hands have very low profiles. In fact, from the side you can just barely see the hands. So I will use a PK-style low profile crystal to celebrate this watch's thin-ness.
It's actually a pretty large crystal. This watch is a little bigger than your typical pre-1969 model. 30.8mm will do the trick.
With a new crystal and a fresh lizard strap, this Thinline 912373 looks and runs like a brand new watch. It's a sharp looking watch, especially for something from the 1970s.