a b

Make the wood that is opened by the wedge open into its mother [socket] in the direction of the length along which the wood grows, so that this hollow does not grow and shrink. And also arrange that this foot never touches the bottom of its cavity, so that it can always, by percussion, be driven back inward. And because the opening of this foot is made along the length of the wood that receives it, that hole will never split.

This is the pivot of a compass, and it must be dry, and then boiled in wax, so that damp can never make it swell, nor dryness shrink it, and it will be perfect. And if you wished to make the pivots of carts in this way, it would also be good, but have them boiled in linseed oil or tallow. But I remind you well to arrange that the planes a b do not touch once they have closed the compass, so that as the compass wears down you can always tighten it with a small blow. And likewise arrange that the slit, or rather the head of the slit, of that male piece which receives the wedge into itself does not touch the bottom of its female, and thus you will always be able to tighten your compass, which will then be harder to open and to close.

This is the way to set one piece of wood into another so that it can never be pulled out of its hole. As it would be to set the leg into a little stool.

This is done only to show you how you would have to proceed when you wish that the pivot of the compass, being of two pieces, should have each of its parts turn with its own arm of the compass as the compass opens. So that in this way the pivot remains, as regards turning around, as if of one piece. And if you do not wish to do this, make the male square and the female likewise square.

This one cannot turn upon itself, only because it has the male and its female square, as is shown in this figure.