CXLII. These are the forms of the double Screws, mentioned before in the Joyners Bench, numb. 139. they are made of Spar, the Screws are fitted with holes or Screw Boxes in the Spars fit to receive them, which being turned, the two pieces are drawn together so hard, that they hold firmly any thing set between them.
In the Sinister Base is set the form of a Plain Iron, (such Plains I mean) as are to plain Boards smooth; for other Plain Irons are cut with squares and half rounds and after the form of an [character of an “S” on its side] according to their Operations.
— From Randle Holme’s “The Academy of Armory, or, A Storehouse of Armory and Blazon” Book III, Chapter VIII, Plate 2.