Apart from the more-or-less subtle differences in dyes used by the different mills, the thread counts can vary rather widely. This is less true of tartans that were designed in the days of tartan registers, but for tartans that have been around since the 19th century the difference in the proportions of the stripes can be striking.

I thought the Hay tartan was the ugliest tartan I had seen when I saw a photograph of it in Scottish Clans & Tartans. That was probably Strathmore's version of the tartan. Later on I saw a photograph of the Hay tartan in a Scottish Lion catalog and decided it was actually quite handsome. There the tartan was probably woven by either Ingles & Buchan or Lochcarron.

The modern introduction of tartan registers with standardized thread counts should have an effect on tartan thread counts similar to the effect the introduction of English dictionaries had on spelling—at least, in the days before the Internet.