Wrist Watch
Wrist Watch
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 Hotsale Stylish Teenager Unisex Leatheroid Wristwatch UVH  US $2.75
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 New Iron Maiden Ed Force One Stainless Wrist Watch US $11.03
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 VINTAGE SWISS MADE ROAMER SEAROCK WRISTWATCH,GREAT US $180.00
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 Unique Bling Crystal Brown Leather Lady Girls Watch New US $1.56
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 I Love You Blue Faux Leather Band White Dial Watch US $7.94
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 New Colorful Tropical Fish Harmony Wrist Watch US $11.03
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 Red Cute Fashion Mens Teenagers Women Lady Unisex Jelly Wrist Watch, CCL US $.99
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 5PCS Lovely HelloKitty Crystal Women Lady Girl Wrist Watch, Xmas Gift, K20-5 US $.99
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What does 21 jewels mean in an automatic wrist watch?
Before quartz and atomic wrist watches, there were automatics. What is the function of jewels in these watches????
Reducing friction is an extremely important goal in watchmaking. Jewels have two important properties that help reduce friction. First, they can be made to be very smooth, and therefore they let the metal parts slide easily. Secondly, they are very hard and therefore don't wear down very quickly. The gears in a watch are carefully designed so that the teeth roll on each other, rather than sliding. If the axle of a gear wears away the hole that it sit in, the gear will shift. That means the teeth will no longer roll on each other and therefore friction will be increased.
Much more info at the link below.