Door hardware and a screw-press: locks, bolts and force
A door that opens from any side; catches for strong doors; the multiplied force of a screw
The upper right of the sheet shows a tall apparatus built around a screw (vite), annotated with a rising series of numbers — 400, 200, 80000, 250000 — that reckon the multiplied force a screw can exert at a and b. Below are door fittings: a horizontal bolt, a rectangular door shown in plan with its hinges and latches, and a column of stacked lock parts. Captions note that these bolts are for strong doors, that one catch keeps an open door from being carried away, and describe a door that opens from every side by turning either the ring r or the knob h.
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The multiplied force of a screw
The upper apparatus centres on a screw (vite) between points a and b, annotated with mounting figures — 400, 200, 80000, 250000. These numbers reckon how greatly the screw multiplies force.
A door that opens from every side
Turning the ring r opens the door at n m, while turning the little knob h opens it on the side f S; Leonardo judges it sound and useful. The latch-bolt of r must be jointed, and that joint must sit opposite the seam of the door.
Bolts for strong doors, and a catch to hold them open
The stacked fittings at the right are used for strong doors. One of them is made so that doors standing open are not carried away.