Calibre 661 — the 660 with 24 jewels

In brief

Seven more jewels than the 660 carries, on the same ladies' base: the 661 takes the count to 24, putting bearings at more points of the going train and cutting friction where they sit.

Short history

The logic was industrial. One set of bridges, wheels and jewelling served both the automatic 5xx calibres and the manual 6xx, so fewer distinct components moved through the factory — and the consequence, decades later, is that parts still cross between the two families. The 661's 24 jewels sit inside that shared architecture rather than a special one. Straightforward, undemanding and common in the Genève and De Ville of the day, it stayed in production until the manual series was wound up in 1974, quartz by then ruling the Swiss market.

Watches that used it

• Omega ladies' watch (1960s)