Understanding Watch Crystal Measurements on Vintage French-Made Glass for Pocket Watches

Watch crystals are important parts of a watch—they protect the face and hands while allowing you to see the time clearly. When you buy unused vintage (new old stock) mineral glass crystals for pocket watches, you’ll often find size information printed on stickers attached to the glass. These stickers usually show two different sizes, which can be confusing.

 

Numbers X/16 Ligne System

Numbers X/8 Ligne System

Diameter in Millimetres (mm)

13

6

29.325

13 1/16

6 1/8

29.466

13 2/16

6 2/8

29.608

13 3/16

6 3/8

29.748

13 4/16

6 4/8

29.889

13 5/16

6 5/8

30.030

13 6/16

6 6/8

30.172

13 7/16

6 7/8

30.313

13 8/16

7

30.453

13 9/16

7 1/8

30.594

13 10/16

7 2/8

30.735

13 11/16

7 3/8

30.876

13 12/16

7 4/8

31.017

13 13/16

7 5/8

31.158

13 14/16

7 6/8

31.299

13 15/16

7 7/8

31.440

14

8

31.581

14 1/16

8 1/8

31.722

14 2/16

8 2/8

31.863

14 3/16

8 3/8

32.004

14 4/16

8 4/8

32.146

14 5/16

8 5/8

32.286

14 6/16

8 6/8

32.427

14 7/16

8 7/8

32.568

14 8/16

9

32.710

14 9/16

9 1/8

32.850

14 10/16

9 2/8

32.991

14 11/16

9 3/8

33.132

14 12/16

9 4/8

33.273

14 13/16

9 5/8

33.414

14 14/16

9 6/8

33.555

14 15/16

9 7/8

33.696

 

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