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Deciphering Watch Crystal Sizes: The X/16 and X/8 Ligne Systems

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V.T.F. Crystal Showing Different Diameter Measurements in Lignes
V.T.F. Crystal Showing Different Diameter Measurements in Lignes

Watch crystals are a critical component of timepieces, offering both a clear view of the watch’s face and protection for the delicate hands and dial. The size of these crystals is typically indicated on stickers adhered to the glass crystals when new. These stickers usually display at least two measurements, one on top and one below, leading to confusion regarding the correct measurement to use when selecting a crystal.


The Ligne: A Brief History

The Ligne is a traditional unit of measurement used in watchmaking. It originated in France and was formally defined during the French Revolution as 1/12th of a ‘Pouce‘, the French equivalent of an inch. This made it equal to 2.2558291 millimeters, and this measurement has been used in the watchmaking industry ever since.

The term ‘Ligne‘ comes from the Latin ‘linea‘, meaning ‘line‘. In its original context, it referred to one of the lines that were used in the typefaces of early printing presses. However, it was adopted by the watchmaking industry due to its suitability for measuring the components used in timepieces.


The X/16 Ligne System

The X/16 Ligne system, as the name suggests, divides the Ligne into 16 parts. This means that each increment in this system is equivalent to about 0.141 mm. This system is often used for its precision, as it allows for more accurate measurements of watch crystal sizes.

On the stickers attached to the watch crystals, the X/16 measurement is usually displayed on top. For example, a sticker might read “13 3/16,” indicating a diameter of 13 and 3/16 Lignes.

The X/16 system is generally considered the standard method for measuring watch crystals due to its precision and wide adoption. For this reason, the older X/8 system is largely ignored when selecting a crystal. However, understanding the X/8 system can still be useful in understanding the alternative measurements used for crystals.


The X/8 Ligne System

The X/8 Ligne system, on the other hand, divides the Ligne into 8 parts. Each increment in this system is equivalent to about 0.282 mm. This system is based on an older Ligne system variation with a different zero point. Size 0 in the X/8 system is equivalent to 10 Lignes, and each full-size increment corresponds to half a Ligne.

On the stickers attached to the watch crystals, the X/8 measurement is usually displayed below the X/16 measurement. For example, a sticker might read “13 3/16” on top and “14 5/8” below, indicating a diameter of 14 and 5/8 Lignes according to the X/8 system.


Crystal Height

In addition to the diameter, the stickers on watch crystals often also display a third number corresponding to the crystal’s height. This height is usually expressed as a whole number between 1 and 8, with 1 indicating a taller crystal and 8 indicating a shorter one. The crystals with a lower height and a greater number are typically used for hunting cases, where the crystal needs to fit with a low profile inside the case when it’s closed.


Illustration Showing the Different Crystal Measurements
Showing the Different Crystal Measurements

Conclusion

Understanding the measurements on the stickers attached to watch crystals can be a bit tricky, especially considering the variations in the Ligne system. However, with a bit of knowledge about the origins and uses of the Ligne, as well as the X/16 Ligne system, it becomes much easier to decipher these measurements and understand the size and height of the watch crystal you’re dealing with. Although the X/8 system is largely ignored in modern watchmaking, it can still be useful when dealing with older timepieces.


Crystal Conversion Table: X/16 Ligne vs. X/8 Ligne vs. Millimeters

X/16 Ligne SystemX/8 Ligne Systemmm
100 0/822.558291
10 1/160 1/822.699280318750000
10 2/160 2/822.8402696375
10 3/160 3/822.981258956250000
10 4/160 4/823.122248275
10 5/160 5/823.263237593750000
10 6/160 6/823.4042269125
10 7/160 7/823.545216231250000
10 8/16123.68620555
10 9/161 1/823.827194868750000
10 10/161 2/823.9681841875
10 11/161 3/824.109173506250000
10 12/161 4/824.250162825
10 13/161 5/824.391152143750000
10 14/161 6/824.5321414625
10 15/161 7/824.673130781250000
11224.8141201
11 1/162 1/824.955109418750000
11 2/162 2/825.0960987375
11 3/162 3/825.237088056250000
11 4/162 4/825.378077375
11 5/162 5/825.519066693750000
11 6/162 6/825.6600560125
11 7/162 7/825.801045331250000
11 8/16325.94203465
11 9/163 1/826.083023968750000
11 10/163 2/826.2240132875
11 11/163 3/826.365002606250000
11 12/163 4/826.505991925
11 13/163 5/826.64698124375
11 14/163 6/826.7879705625
11 15/163 7/826.92895988125
12427.069949200000000
12 1/164 1/827.21093851875
12 2/164 2/827.351927837500000
12 3/164 3/827.49291715625
12 4/164 4/827.633906475000000
12 5/164 5/827.77489579375
12 6/164 6/827.915885112500000
12 7/164 7/828.05687443125
12 8/16528.197863750000000
12 9/165 1/828.33885306875
12 10/165 2/828.479842387500000
12 11/165 3/828.62083170625
12 12/165 4/828.761821025000000
12 13/165 5/828.90281034375
12 14/165 6/829.043799662500000
12 15/165 7/829.18478898125
13629.325778300000000
13 1/166 1/829.46676761875
13 2/166 2/829.607756937500000
13 3/166 3/829.74874625625
13 4/166 4/829.889735575000000
13 5/166 5/830.03072489375
13 6/166 6/830.171714212500000
13 7/166 7/830.31270353125
13 8/16730.453692850000000
13 9/167 1/830.59468216875
13 10/167 2/830.735671487500000
13 11/167 3/830.87666080625
13 12/167 4/831.017650125000000
13 13/167 5/831.15863944375
13 14/167 6/831.299628762500000
13 15/167 7/831.44061808125
14831.581607400000000
14 1/168 1/831.72259671875
14 2/168 2/831.863586037500000
14 3/168 3/832.00457535625
14 4/168 4/832.145564675
14 5/168 5/832.286553993750000
14 6/168 6/832.4275433125
14 7/168 7/832.56853263125
14 8/16932.70952195
14 9/169 1/832.850511268750000
14 10/169 2/832.9915005875
14 11/169 3/833.13248990625
14 12/169 4/833.273479225
14 13/169 5/833.414468543750000
14 14/169 6/833.5554578625
14 15/169 7/833.69644718125
151033.8374365
15 1/1610 1/833.978425818750000
15 2/1610 2/834.1194151375
15 3/1610 3/834.26040445625
15 4/1610 4/834.401393775
15 5/1610 5/834.542383093750000
15 6/1610 6/834.6833724125
15 7/1610 7/834.82436173125
15 8/161134.96535105
15 9/1611 1/835.106340368750000
15 10/1611 2/835.2473296875
15 11/1611 3/835.38831900625
15 12/1611 4/835.529308325
15 13/1611 5/835.670297643750000
15 14/1611 6/835.8112869625
15 15/1611 7/835.95227628125
161236.0932656
16 1/1612 1/836.234254918750000
16 2/1612 2/836.375244237500000
16 3/1612 3/836.51623355625
16 4/1612 4/836.657222875
16 5/1612 5/836.798212193750000
16 6/1612 6/836.939201512500000
16 7/1612 7/837.08019083125
16 8/161337.22118015
16 9/1613 1/837.362169468750000
16 10/1613 2/837.503158787500000
16 11/1613 3/837.64414810625
16 12/1613 4/837.785137425
16 13/1613 5/837.926126743750000
16 14/1613 6/838.067116062500000
16 15/1613 7/838.20810538125
171438.3490947
17 1/1614 1/838.490084018750000
17 2/1614 2/838.631073337500000
17 3/1614 3/838.77206265625
17 4/1614 4/838.913051975
17 5/1614 5/839.054041293750000
17 6/1614 6/839.195030612500000
17 7/1614 7/839.33601993125
17 8/161539.47700925
17 9/1615 1/839.617998568750000
17 10/1615 2/839.758987887500000
17 11/1615 3/839.89997720625
17 12/1615 4/840.040966525
17 13/1615 5/840.18195584375
17 14/1615 6/840.322945162500000
17 15/1615 7/840.46393448125
181640.6049238
18 1/1616 1/840.74591311875
18 2/1616 2/840.886902437500000
18 3/1616 3/841.02789175625
18 4/1616 4/841.168881075
18 5/1616 5/841.30987039375
18 6/1616 6/841.450859712500000
18 7/1616 7/841.59184903125
18 8/161741.73283835
18 9/1617 1/841.87382766875
18 10/1617 2/842.014816987500000
18 11/1617 3/842.15580630625
18 12/1617 4/842.296795625
18 13/1617 5/842.43778494375
18 14/1617 6/842.578774262500000
18 15/1617 7/842.71976358125
191842.8607529
19 1/1618 1/843.00174221875
19 2/1618 2/843.142731537500000
19 3/1618 3/843.28372085625
19 4/1618 4/843.424710175
19 5/1618 5/843.56569949375
19 6/1618 6/843.706688812500000
19 7/1618 7/843.84767813125
19 8/161943.98866745
19 9/1619 1/844.12965676875
19 10/1619 2/844.270646087500000
19 11/1619 3/844.41163540625
19 12/1619 4/844.552624725
19 13/1619 5/844.69361404375
19 14/1619 6/844.834603362500000
19 15/1619 7/844.97559268125
202045.116582
20 1/1620 1/845.25757131875
20 2/1620 2/845.398560637500000
20 3/1620 3/845.539549956250000
20 4/1620 4/845.680539275
20 5/1620 5/845.82152859375
20 6/1620 6/845.962517912500000
20 7/1620 7/846.103507231250000
20 8/162146.24449655
20 9/1621 1/846.38548586875
20 10/1621 2/846.526475187500000
20 11/1621 3/846.667464506250000
20 12/1621 4/846.808453825
20 13/1621 5/846.94944314375
20 14/1621 6/847.090432462500000
20 15/1621 7/847.231421781250000
212247.3724111
21 1/1622 1/847.51340041875
21 2/1622 2/847.654389737500000
21 3/1622 3/847.795379056250000
21 4/1622 4/847.936368375
21 5/1622 5/848.07735769375
21 6/1622 6/848.218347012500000
21 7/1622 7/848.359336331250000
21 8/162348.50032565
21 9/1623 1/848.64131496875
21 10/1623 2/848.782304287500000
21 11/1623 3/848.923293606250000
21 12/1623 4/849.064282925
21 13/1623 5/849.20527224375
21 14/1623 6/849.346261562500000
21 15/1623 7/849.487250881250000
222449.6282402
22 1/1624 1/849.76922951875
22 2/1624 2/849.910218837500000
22 3/1624 3/850.051208156250000
22 4/1624 4/850.192197475
22 5/1624 5/850.33318679375
22 6/1624 6/850.474176112500000
22 7/1624 7/850.615165431250000
22 8/162550.75615475
22 9/1625 1/850.89714406875
22 10/1625 2/851.038133387500000
22 11/1625 3/851.179122706250000
22 12/1625 4/851.320112025
22 13/1625 5/851.46110134375
22 14/1625 6/851.602090662500000
22 15/1625 7/851.743079981250000
232651.8840693

4 Comments

  1. Excellent piece on old glass pocket watch crystals.
    I am a retired AWI/AWCI certified master watchmaker and over the years, I have collected a BUNCH of these old glass crystals from the older generation of watchmakers.
    Worth mentioning is the foggy splotch that’s sometimes is under the label. Some people think these are ruined. No. Cerium oxide on a 1″ felt buff. Make the Cer Ox into a paste similar to toothpaste. Apply to the stain and buff. This takes about 30 seconds and will remove the “sticker bite” and make the crystals really shine.

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