Thin-o-matic TM-2800
1968–1970 · 14k Solid Yellow Gold · Automatic
About the Thin-o-matic TM-2800
Made from 1968 through 1970, the Thin-o-matic TM-2800 is part of Hamilton's Thin-o-matic family, which was built around the goal of producing genuinely slim automatic wristwatches at a time when automatic movements were typically much thicker. The TM-2800 pairs a 14k solid yellow gold round case with a silver dial carrying Arabic numerals and a sweep seconds hand, all powered by Hamilton's caliber 628, a 17-jewel automatic. The all-gold presentation gives it a dressy character that fits the Thin-o-matic line's position as Hamilton's more formal automatic offering.
Solid 14k gold cases from this era can vary considerably in condition, so close attention to the lugs is worthwhile. The case profile is straight-lugged and round, which means wear tends to concentrate at the lug tips and case flanks. A silver dial with Arabic numerals on a gold case is a clean, readable combination, and original dials in good shape add meaningfully to what the watch is worth.
From the Catalog
Hamilton described the TM-2800 simply as an ultra-thin 14k yellow gold watch, priced at $175, which reflected both the solid gold case and the engineering behind the slim caliber 628 movement.
Hamilton Catalog Images
1968
What to Look For
| Dial | Look for even color across the silver dial surface. Spotting, peeling near the edges, or discoloration around the Arabic numerals are common with dials this age. An original dial in honest condition is worth preserving. |
| Crystal | Check for deep scratches or crazing in the crystal. A replacement acrylic is usually straightforward, but confirm the correct profile for this round case before sourcing one. |
| Movement | The caliber 628 micro-rotor is a delicate mechanism, and parts for the rotor assembly are no longer available. Also watch for the cannon pinion issue common to offset center wheel designs on these movements: if the hands are not advancing even though the movement is running, a loose cannon pinion is often the cause. Dried lubricants can also create enough drag to stop the movement entirely, so a full service is usually the right starting point. |
| Case | Solid 14k gold cases polish beautifully but can be over-polished to the point where the original case lines are softened or lost. Look at the lug tips and case edges to get a sense of how many times this one has been through a polishing wheel. The case back on Thin-o-matics can be tight and requires the right tools to open without damage. |
| Crown | Test the crown through all positions. Sticky or stiff crown action on a watch this age often points to a dried gasket or a stem that needs attention. This watch was originally rated weatherproof, but that rating does not hold after decades without a service, so keep it away from water regardless. |
The Movement
The caliber 628 is a micro-rotor automatic, meaning the winding rotor sits flush within the movement rather than sweeping across the full diameter as a conventional rotor would. That design choice is what allows the Thin-o-matic to be as slim as it is. It runs 17 jewels and is a genuinely compact movement, though that compactness comes with the caveat that parts, particularly for the micro-rotor assembly, are increasingly difficult to source.