Hodgson, The Steel Square.

Wheeler, p. 465.

Tate, pp. 21-25.

Building Trades Pocketbook, pp. 234-237.

Selden, pp. 149, 150-152, 175.

Sargent's Steel Squares.

(9) Sharpening Tools.

Barnard, pp. 136-142.

Sickels, pp. 80-85.

Wheeler, pp. 480-488.