Automatic K-406
1956–1957 · 10k Yellow Gold Filled · Automatic
About the Automatic K-406
Made from 1956 through 1957, the Automatic K-406 is part of Hamilton's broader Automatic family, a line that brought self-winding convenience to American watch buyers in the postwar years. It runs on the caliber 661, a 17-jewel automatic movement, and comes in a round 10K yellow Gold Filled case with a white dial featuring embossed gold numerals and markers, luminous dots at the hour positions, and a pearled track. Hamilton marketed it as waterproof and offered it on either a strap or bracelet, with the bracelet configuration carrying a slightly higher price.
Embossed dials like this one age differently than printed dials, and finding an example where the numerals and markers are still crisp and undamaged is genuinely satisfying. The luminous dots are worth a close look, as old radium or tritium lume can mottle or discolor over the decades, and that affects the overall presentation more than most people expect. The pearled track is a small detail that often gets overlooked, but it gives the dial real depth and is easy to damage during a careless service.
From the Catalog
Hamilton's 1956 catalog described the K-406 as having a 10K yellow gold-filled case with yellow embossed numerals and markers, luminous dots, and a pearled track, and listed it as waterproof. It was priced at $89.50 on a strap and $100.00 on a bracelet.
Hamilton Catalog Images
1956
1957
What to Look For
| Dial | Look carefully at the embossed numerals and markers under good light. Chips, flaking, or wear to the raised surfaces are common and hard to restore convincingly. Check the luminous dots for heavy discoloration or crumbling, and look at the pearled track to make sure it hasn't been damaged or polished flat during a past service. |
| Crystal | This case opens through the crystal rather than the case back, which is not obvious from the outside. Look for scratches or tool marks around the crystal edge and bezel, which often indicate someone tried to pry the case back instead. |
| Movement | Ask about service history. Oil dries out on any automatic that has sat for years, and enough friction builds up to stop the rotor and prevent the mainspring from winding. A watch that only runs when manually wound but stops with normal wear is a reliable sign it needs attention. |
| Case | Gold-filled cases from this era show wear at the lugs and high contact points first. Check for brass showing through at the lug tips and around the crown tube. Swept lugs like these are difficult to replate convincingly, so buy the condition you can live with. |
| Crown | Hamilton listed this watch as waterproof, but that rating depended on gaskets that are now decades old and almost certainly compromised. Do not assume any water resistance, and check that the crown seals properly against the case without wobble or looseness. |
The Movement
The caliber 661 is a 17-jewel automatic that winds through a rotating oscillating weight, so normal wrist movement keeps it running without any need to wind the crown. It is a solid and well-regarded movement in Hamilton's American-era automatic lineup, capable of good accuracy when properly serviced. Oil dries and thickens over time, and on unserviced examples that friction can become enough to stop the watch entirely.