Thin-o-matic T-501
1959–1962 · Stainless · Automatic
About the Thin-o-matic T-501
The Thin-o-matic T-501 was one of the founding models of Hamilton's Thin-o-matic line, produced from 1959 through 1962. It runs on either the caliber 663 or 666, both 17-jewel automatic movements that allowed Hamilton to offer a genuinely slim wristwatch at a time when thin cases were very much in demand. The stainless steel case is round, measuring 34mm wide and 10mm thick, with a sweep seconds hand and a dial featuring embossed white numerals and luminous markers on a pearled track. A black dial variant joined the lineup in 1960, giving collectors two distinct versions to look for.
Finding a T-501 with its original dial in solid shape is the real challenge. The embossed numerals and luminous markers on these dials are prone to flaking and fading, and the pearled track can show wear that's easy to overlook in poor lighting. Black dial examples are the less common of the two and tend to generate more interest when they surface in good condition.
From the Catalog
Hamilton's 1959 catalog described the T-501 as offering embossed white numerals and luminous markers with a pearled track, available on white or black dial, in a waterproof stainless steel case. It retailed for $79.50 at introduction.
Hamilton Catalog Images
1959
1960
1961
What to Look For
| Dial | Look closely at the embossed numerals and luminous markers under good light. Chips or losses in the embossed finish are common and often underreported. Check the pearled track for consistent texture around the entire perimeter, and look for any fading, spotting, or moisture damage on both white and black dial examples. |
| Crystal | These watches take a acrylic crystal. Light scratches can be polished out, but deep gouges or crazing mean a replacement is needed. Make sure the crystal sits flush and hasn't been pushed in or seated improperly from a previous replacement. |
| Movement | The caliber 663 and 666 share an architecture where the wheel arbors are long and require precise alignment when the movement bridges are reinstalled. Sloppy service work often results in a watch that runs poorly or stops intermittently. Ask about service history and, if possible, observe the rotor. A rotor that wobbles, drags, or spins unevenly may indicate a bent rotor framework, which is a known issue on these movements and requires careful attention during repair. |
| Case | Check the case edges and lugs for signs of over-polishing. The round 34mm case can lose its original profile quickly if a jeweler has buffed aggressively. The caseback should be tight and show no signs of forced opening. |
| Crown | The crown should screw down or seat firmly and operate smoothly through the winding positions. A mushy or stiff crown can point to a worn or damaged stem, which may be a sourcing challenge given the age of these movements. |
The Movement
The caliber 663 and 666 are Swiss-made 17-jewel automatic movements built around a micro-rotor design, which allowed the overall case to stay thin without sacrificing the convenience of automatic winding. Both calibers are functionally similar in architecture, though there are internal differences in their construction. They are capable everyday movements when properly serviced, but the long wheel arbors require care during reassembly, making a quality service more demanding than average.