Self-closing door latches, hinge-straps and screw fittings
Springs and bolts; where to apply force on a pivoted bar; the female thread of a screw
This page collects a family of iron fittings: a small hooked latch, a long hinge-strap (bandella), a worm-and-rack with its cylindrical female thread, and a T-shaped bolt with a barrel. Text explains that to move a bar f S toward r one should apply the spring high, far from the pivot S where resistance is least, rather than low near the pivot. A series of four self-closing door bolts labelled a, b, c, d is discussed, and one fitting is noted as serving chimney-workers who insert interchangeable rods into a single socket.
On this page
Apply the spring far from the pivot of the bar
To move the bar f S toward r with the mover m b, one may start high at a and descend to b, or start low and rise. Beginning low at b puts the spring near the pivot where resistance is great; beginning high, far from the pivot S, is easy, so it is better to begin from above.
The female thread that receives the male b
The strap shown serves as the female socket for the male part b figured below it. A separate note labels the cylindrical piece the female of the screw.
A turning socket for chimney-workers' rods
This fitting is used by those who work at chimneys. It lets various little rods be set into one and the same hole and held firm while turning, as if the whole were born of a single piece.
Four self-closing door bolts a, b, c, d
Four ways of making doors that shut by themselves are compared, the topmost being the best. One with thick, wide edges and a wide single ring around the male is judged useful and much shorter, since the ring needs no female cut for a screw; the lowest, however, will soon be cut through by its ring.