I'm surprised that no-one has made the connection with the 'rule' for wearing a sgian dubh.

The rule to which I refer is of course an invention based on standardised military rules that exist to ensure uniformity. I don't wear either sgian dubh or fly plaid but when I used to wear the former I wore it on my left b because I'm left handed.

Fly plaids are of course a pseudo relic of the upper portion of a belted plaid which was generally fastened to the left shoulder in order to leave the sword arm unencumbered. The left-handed swordsman would naturally have fastened his plaid to his right shoulder.

Bottom line, unless one is in the military or some other group that insists on standardisation then there is no hard and fast rule so if one wishes to wear either a sgian dubh or fly plaid then where t on the side that is most practice.