Thinline 6510
1968–1970 · 10k RGP / Stainless · Manual Wind
About the Thinline 6510
The Thinline 6510 appeared in a single catalog year, 1968, as part of Hamilton's Thinline family, a series defined by slim profiles and clean, modern proportions. The case is 10K yellow RGP with a stainless steel back, round in shape with swept lugs, and inside runs the caliber 639, a 17-jewel manual wind movement. The dial is silver with applied gold numerals at 3, 6, 9, and 12, applied gold markers filling the remaining hour positions, and a subseconds register at the expected position. Some examples show a radial finish to the silver dial, which catches light differently and gives the watch a noticeably more dynamic look.
Radial-finish dials are worth seeking out specifically on this reference, since the texture adds depth that the flat silver version lacks. The applied gold numerals and markers hold up well over time but can pull away from the dial at the edges on heavily worn examples, so a close look with good light is worthwhile. Finding a clean one with both the dial and the RGP finish in good shape is a small but satisfying achievement given how briefly this model was available.
From the Catalog
Hamilton listed the Thinline 6510 in 1968 at $49.95 on strap and $59.95 with bracelet, positioning it as an accessible entry into the Thinline range with a clean round case and yellow gold finish.
Hamilton Catalog Images
1968
What to Look For
| Dial | Check the applied gold numerals and markers carefully. Separated or shifted indices are a common issue on watches this age and are difficult to correct without a dial restoration. Also confirm whether the dial has a radial finish or a flat silver finish, since that affects both desirability and value. |
| Crystal | Look for chips, deep scratches, or a hazy appearance. Replacement crystals are available for round cases like this, but a well-fitting original-style crystal makes a difference in how the watch presents. |
| Movement | The caliber 639 has very little clearance between its overlapping parts, and oil in a movement this age has almost certainly dried out. Dried lubricant creates enough friction to stop the watch or degrade accuracy significantly. Ask whether the movement has been recently serviced and by whom. |
| Case | Examine the 10K yellow RGP surface for wear-through to the base metal, particularly on the lugs and case sides. Some wear is expected, but heavy brass showing through affects both appearance and resale value. The case back can be tricky to open, so check for tool marks around the edge. |
| Crown | Work the crown through both winding and setting positions. It should feel smooth in each position with no grinding or slipping. A worn or replaced crown on a watch like this is a minor concern, but a damaged stem underneath is a more meaningful repair. |
The Movement
The caliber 639 is a 17-jewel manual wind movement made for Hamilton during its Swiss production period. It winds from the crown, keeps time across a traditional gear train, and drives a subseconds hand from a separate wheel at the bottom of the dial. The 639 is a competent, repairable movement, though its tight internal tolerances mean a careful, experienced hand matters when it comes time for service.