Thin-o-matic T-415
1965–1967 · 10k YGF · Automatic
About the Thin-o-matic T-415
The Thin-o-matic T-415 was produced from 1965 through 1967, placing it squarely in the period when Hamilton was refining its Swiss-made automatic lineup under the Thin-o-matic name. The case is 10k yellow Gold Filled with a round profile and straight lugs, housing the 17-jewel caliber 623 automatic movement. Within the Thin-o-matic family, the T-415 represents the more accessible end of the range, offered at a price point below the solid gold versions while sharing the same slim automatic movement. A 1966 catalog lists it at $115 on bracelet or $99.50 on strap, and an earlier 1965 listing describes a silver dial with gold markers.
Finding a clean T-415 takes some patience. The Gold Filled cases on these hold up well when they haven't been polished aggressively, but the edges and lugs are the first places to show wear, so check those carefully before assuming a case is in good shape. The 1965 catalog notes a silver dial with gold markers, which differs from later gold-dialed examples, so dial variation is worth paying attention to when comparing examples.
From the Catalog
Hamilton's 1966 catalog offered the T-415 in 10k yellow gold fill at $115 on bracelet or $99.50 on strap, positioning it as a wearable everyday automatic for someone who wanted the Thin-o-matic look without stepping up to solid gold pricing.
Hamilton Catalog Images
1966
What to Look For
| Dial | Check for spotting, fading, or separation around the hour markers. The 1965 catalog describes a silver dial with gold markers, while later versions appear in gold. If the seller isn't sure which variant they have, look closely at the dial color in natural light rather than relying on photos alone. |
| Crystal | Look for deep scratches or crazing in the acrylic crystal. A hazy or scratched crystal is replaceable, but confirm it hasn't been substituted with an ill-fitting generic before buying. |
| Movement | Ask when the caliber 623 was last serviced. One practical thing to know: the stem for this movement was discontinued long ago and is genuinely hard to source now. Before purchasing, confirm the crown engages smoothly and the stem is original and intact, because finding a replacement is not straightforward. |
| Case | Examine the lugs and case edges for heavy wear through the gold fill. Some wear is expected on a 60-year-old watch, but deep wear exposing brass underneath affects both appearance and value. Also be aware that the case back on these can be tricky to open without the right tools, so don't assume it hasn't been opened just because it looks undisturbed. |
| Crown | The crown should screw or press down firmly and pull out to the time-setting position cleanly. Any looseness or wobble may indicate a damaged or mismatched stem, which as noted above is not easy to replace. |
The Movement
The caliber 623 is a 17-jewel Swiss automatic movement that Hamilton used across several Thin-o-matic models in the mid-1960s. It winds via a bidirectional rotor and drives a sweep seconds hand, giving the dial a clean, uninterrupted look. Like most movements of this age, it performs best when it has been recently serviced, since decades-old oil thickens and creates enough drag to affect accuracy or stop the watch entirely.