Automatic K-100
1955–1957 · 18k Solid Yellow Gold · Automatic
About the Automatic K-100
Made from 1955 through 1957, the Automatic K-100 is part of Hamilton's Automatic family, a line of self-winding dress watches that leaned heavily into the luxury end of the market. This one came in an 18K yellow gold case and ran on the caliber 661, a 17-jewel automatic movement with sweep seconds. The dial is silver with applied gold numerals at the even-numbered positions, applied gold markers, and a pearled minute track, giving it a refined, unhurried look that matched the price point.
At $225 in 1955, this was a serious purchase, and most examples that have survived did so in someone's jewelry box rather than a daily rotation, which works in a buyer's favor. The dial variants are worth knowing: some examples show solid 18K numerals and markers with lines extending inward from the hour markers, while others have the luminous marker treatment described in Hamilton's original marketing. Either way, the pearled minute track is a signature detail on this model, and its condition is one of the first things to check.
From the Catalog
Hamilton described the K-100 as offering an 18K yellow gold case with sweep seconds, 18K gold numerals, luminous markers, and a pearled track, and listed it as anti-magnetic, shock resistant, and waterproof. It retailed for $225 in 1955.
Hamilton Catalog Images
1955
1957
What to Look For
| Dial | Look closely at the pearled minute track. The individual pearl details are small and delicate, and any cleaning or mishandling over the decades can flatten or damage them. Also check for discoloration or burn marks near the center, which can happen when hands sit too close to the dial surface over long periods. |
| Crystal | This case opens through the crystal rather than the case back. Look around the crystal edge for pry marks, chips, or uneven seating, which often indicate someone tried to open it from the wrong side. |
| Movement | Dried oil is a real concern on any caliber 661 that has sat unserviced for years. Enough friction from dried lubricants will stop the movement entirely. Ask about service history and, if unknown, budget for a full service before regular wear. |
| Case | The 18K yellow gold case should show its age gracefully, but check the lugs and case sides for deep gouges from improper opening attempts. Light wear is expected and honest; tool marks near the bezel or case back joint are a red flag. |
| Crown | Check that the crown screws or seats properly and that the stem engages smoothly into the setting position. A sticky or loose crown can indicate stem wear or a damaged setting mechanism inside the movement. |
The Movement
The caliber 661 is a 17-jewel Hamilton automatic, powering the watch through a rotor-driven winding system that keeps the mainspring wound through normal wrist movement. It includes sweep seconds, which runs continuously from the center rather than ticking at discrete intervals. It is a capable movement, but like any automatic from this era, it depends on clean, properly viscous lubricants to run reliably.