A bar is inserted through a ring.
I am trying to rewrite the above sentence such that the subject is "a ring". My example is as follows:
A ring is inserted on a bar.
Does my example make sense? Specifically, the inside shape and size of the ring are identical to the outside shape and size of the bar so that they can contact each other all around.
The same relative positions or motions of bar and ring can be achieved by inserting the bar into the ring, or passing the ring over the bar, depending on which of the items is stationary, and which one is movable. You will see phrasings like these in descriptions of experiments in electricity and magnetism.
It was reserved for Faraday to discover, nearly fifty years ago, the law prevailing in these reverse electromagnets. He found [that] when a coil is passed over the poles of a magnetized steel bar, or the steel bar inserted in the coil, an electric current is developed, but lasting only as long as the relative movement of the coil or bar, when the coil or bar is moved in an opposite direction so as to separate them, a temporary current in an opposite direction is developed.
"Bell's Telephone" - The Manufacturer and Builder, Pg. 277, December 1877
Another possibility is:
On page 2 of this article you can find the text quoted below. I think the verb "set" is particularly appropriate to convey the idea of installing the ring and leaving it in place, while "around" is the perfect counterpart of "through" (the bar is inserted through the circular hole of the ring, while the ring is set around the circumferential surface of the bar).
Figure 2 shows a typical cathode temperature distribution measured by a two color pyrometer. As shown in Fig. 1, an iron ring was set around the cathode to eliminate the magnetic field on its surface for electron emission.
It should be kept in mind that, as opposed to "being passed over", which indicates movement, "being set around" suggests that the ring remained in that position after being installed.
You could say
A ring is placed on a bar.
A ring is slipped onto a bar.
Compare:
The groom placed a ring on the bride's finger.
A ring was placed on the bride's finger by the groom.
Frodo slipped the ring onto his finger.
The ring was slipped by Frodo onto his finger.
The passive may seem awkward when there's no clear justification for it.
