Kiernan's suggestion (or rather, insistence), above, that the line usually given as:

'My shoes they are well worn now, my stockings they are thin'

derives from the names for part of a swing plough, is the only time I have heard this. However, I have now found further authority.
An essay about music and song "Along the Annagh Road"(Which is near Granard in Co. Cavan) by one Mary Tiernan, then a pupil of Cnoc Muire Secondary School in Granard, won first prize in a Competition 'Duchas' (Heritage) run by Comhaltas Ceoiltoirí Eireann in 1975. The essay, with a picture of the purported Rocks of Bawn was printed in the magazine 'Treoir' vol. 7 number 5 for Samhain (Hallowe'en approximately)1975.

It gives a text of The Rocks of Bawn, attributing it to Barney Sweeney and giving the usual five stanzas. However, the line corresponding to that I give above reads:

My coulter's very worn now, My sock is very thin

The 'sock' of a plough is an iron plate about nine inches square, slightly concave and sharpened all round to divide the soil horizontally; the coulter is the elaborately curved plate placed at its lowest edge, perpendicular to the sock, that forms the furrow by turning the soil. Thus the line is completely consistent with the theme of the song. The process whereby the trade terms became transformed is well-known to 'folk'.

The final verse asks the Queen of England for support -none of your sergeant-majors on the Annagh Road.