Thin-o-matic TM-5800
1967–1970 · Stainless · Automatic
About the Thin-o-matic TM-5800
The Thin-o-matic TM-5800 was made from 1967 through 1970 in a stainless steel round case, powered by Hamilton's caliber 628 automatic micro-rotor movement. It belongs to the Thin-o-matic family, Hamilton's line of ultra-slim automatics built around the micro-rotor concept to keep overall case thickness to a minimum. The silver dial carries applied markers with no hour numerals and a sweep seconds hand, giving the watch a clean, uncluttered face that suited the dressy, slim-profile aesthetic Hamilton was chasing at the time.
Finding one with the applied markers intact and the silver dial free of spotting or oxidation is the real challenge here. These dials are unforgiving of moisture exposure, and because the markers sit proud of the dial surface, any water intrusion tends to leave visible shadows or separation at the edges. A clean dial on a TM-5800 is genuinely satisfying to come across.
Hamilton Catalog Images
1968
What to Look For
| Dial | Look closely at the applied markers under good light. Check for any separation at the edges or shadow marks beneath them, which usually point to past moisture exposure. The silver dial itself should be even in tone with no spotting or oxidation patches. |
| Crystal | The crystal on these is acrylic. Light surface scratches are normal and can be polished out, but deep gouges or a hazy, crazed surface mean replacement. Make sure it sits flush with no gaps around the edge. |
| Movement | The caliber 628 micro-rotor is the heart of this watch, and parts for the rotor assembly are no longer available. Listen when you move the watch around. The rotor should spin freely and quietly. Any grinding or resistance is a red flag. Also watch the hands: if the movement seems to be running but the hands are not moving, that points to a loose cannon pinion on the offset center wheel, which is a known issue on this caliber. |
| Case | The stainless steel case holds up well over time, but check the lugs for wear and make sure the case back seals properly. These case backs can be stubborn to open without the right tools, and a back that has been pried improperly will show it around the lip. |
| Crown | Work the crown through winding and setting. It should engage cleanly with no slipping or grittiness. Even if the watch was originally rated weatherproof, that designation does not hold after 60-plus years. Keep it away from water. |
The Movement
The caliber 628 is Hamilton's micro-rotor automatic, designed to allow a much thinner movement than a conventional full-rotor automatic could achieve. The rotor sits within the plane of the movement rather than swinging over the top of it, which is what makes the Thin-o-matic profile possible. It runs 17 jewels and is a genuinely elegant piece of engineering, though it asks for careful servicing given the scarcity of replacement parts for the rotor assembly.