Settings > User Settings > Other

Use Ligne (L) for Button Width - Not selected by Default

(mm is the default measurement, if this is not selected)

Ligne - historic unit of length used prior to late 18th century before metric system was adopted. Also referred to as 'line.'

A ligne or line is 1/40th of 1 inch, which is ~0.635 mm.

A button that is 20 ligne or line is 1/2" or 12.7 mm in diameter.

A button that is 40 ligne or line is 1" or 25.4 mm in diameter.

Default Unit of Thread Thickness - Tex (default)

Two methods of calculating thread thickness: Fixed Length and Fixed Weight.

Tex uses the fixed length method. It measures the weight in grams of 1,000 meters of thread. The higher the tex, the thicker the thread.

Denier uses the fixed length method. It measures the weight in grams of 9,000 meters of thread. A higher value is thicker.

Metric uses the fixed weight method. It measures the length of a kilogram of thread. The lower the number, the thicker the thread.

Millimeter is not a standard and probably just refers to the width in 3D.

Ticket is a commercial numbering system. The lower the number, the thicker the thread.