After Pirie's invention of the 3-wheeled plough in 1867 manufacturers soon adopted the principle and made their contributions to its improvement. John Gray's doublefurrow, 3-wheeled plough was the model for Reid and Gray when they made their first "colonial" plough for John Grigg of Longbeach. Top—Pirie's original doublefurrow, 3-wheeled plough, which he patented in 1867. Upper middle— doublefurrow, 3-wheeled plough made by John Gray and used by Reid and Gray as the pattern for their first "colonial" plough. Lower middle—A later model of John Gray's double-furrow, 3-wheeled plough. Bottom—A P. and D. Duncan Ltd. doublefurrow plough which was widely used in the late 1870's and later.

New Zealand Journal of Agriculture, Volume 81, Issue 6, 15 December 1950, Page 510

After Pirie's invention of the 3-wheeled plough in 1867 manufacturers soon adopted the principle and made their contributions to its improvement. John Gray's doublefurrow, 3-wheeled plough was the model for Reid and Gray when they made their first "colonial" plough for John Grigg of Longbeach. Top— Pirie's original doublefurrow, 3-wheeled plough, which he patented in 1867. Upper middle— doublefurrow, 3-wheeled plough made by John Gray and used by Reid and Gray as the pattern for their first "colonial" plough. Lower middle—A later model of John Gray's double-furrow, 3-wheeled plough. Bottom—A P. and D. Duncan Ltd. doublefurrow plough which was widely used in the late 1 870's and later.