As others have said, I look at sett size as a byproduct of cloth weight. The yarns in a 16 oz tartan are thicker than in a 13 oz, so the sett of a 16 oz will necessarily be larger than that of a 13 oz in the same tartan (see illustrations above). Reaching back into tartan history, I've noted that Wilson's & Sons had plaiding and they had kilting setts of the same tartans, and that the kilting setts seemed to be smaller. Figheadair has showed us photos of 18th c. plaids with really large setts (2-1/2 sets to a 27" width), including that tartan set of MacDougall curtains with the 20" sett. Perhaps he could enlighten us on whether there were differences in the sett sizes of kilting and plaiding cloth of the same tartan during the early days of tartan. Thank you in advance!