We currently sell linen thread in four sizes. This photo shows samples, with a millimetre scale (labelled in centimetres) above and an inch scale below.
All sizes are available in 100m rolls or 10m hanks. The 18/3 thread is white while the other three are a more natural tan colour. The 25/3 is lightly waxed; the others are unwaxed but we also sell cakes of beeswax that you can run your thread over before sewing. The wax helps the thread pass through the holes in the paper easier, allows the knots to pull tighter, and lubricates the thread to reduce wear when the binding flexes in use.
For more details on how the size numbering works, see our blog post on the subject.