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The diameter is that of the ring - afaik, will have to look it up. “Wiggle room“ doesn‘t matter as long as the spring length is in the ball park. Essential sizes of a mainspring are thickness, width and length. Diameter is just a hint if you can push into the barrel directly or will need a winder, it is no property of the spring. Frank -
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Hi @Zendoc, I guess you're like me and you don't have a mainspring winder. I searched GR mainspring for the AS 1686 mainspring and I now understand your dilemma. The exact one is discontinued. To answer you question more directly, I see two good alternatives for you: a) GR4485 with 1.60 x .10 x 280 x 8.5 ( I guess this one is the one you found): https://www.cousinsuk.com/sku/details/mainsprings-by-list-watch-pocket/GR4485 OR b) GR4477 with 1.60 x .095 x 320 x 9. https://www.cousinsuk.com/sku/details/mainsprings-by-list-watch-pocket/gr4477 As you know, the the AS 1686 spring is supposed to be 1.60 x .10 x 300 x 9. - both of the above will fit and you'll manage to insert them from the retention ring without need for a mainspring winder (provided you know how to do it). - GR4485 will give you more power (=higher amplitude), but less power reserve (due to shorter length) than the original. - GR4477 will give you the same power reserve as the original. However, a bit less power. Personally, I'd take GR4477 for two reasons: 1. Well, the power reserve is better. 2. With modern lubricants and modern mainspring metal alloys, you tend to get a higher amplitude anyways. You'd maybe even end up with too much amplitude (knocking) if you go with the original size and use thin synthetic oils-- see discussion here: https://www.watchrepairtalk.com/topic/10580-omega-calt17-help/#comment-248101 -
Your setup is correct. The smallest diameter of one pulley must correspond with the largest of the other one, else not speed variation. Frank
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