If they are buckles, the only two ways I can see they’d work (by comparison with other, modern one) are:
(1) -bring the cord or strap in from the side over the ring, let’s say from the left,
– down between it and the left-hand bar of the hinged loop,
– round the back of the loop,
– back up between the right-hand side of the loop and the ring,
– out over that second (RH) “side” of the ring.
It might be locked, rather awkwardly, by taking the free end back round behind everything, up and out leftwards between the strap and ring on the left.
OR
(2)
Referring to the left-hand (obverse) photo
– from the lower margin of the image, through the hinged loop above the ring where stanped with the patent,]
– down between the bars,
– up round the hinge,
– back up to the top and out through the loop above the incoming part of the strap.
I can’t though work out what happens to the other end of the strap – unless that is intended to be looped round part of the buckle and fastened back on itself, rather as on a trouser-belt buckle.
Or Method 1 is used with both ends of the strap threaded from opposite sides.
We might note they appear used, but there are no obvious wear-marks on any part of them. Though they might not have been intended for frequent use – instead would be set and left for some indeterminate time.
Try it with some suitable material, bearing in mind synthetic-material straps are much more likely to slip than the leather or canvas webbing they were likely made to hold. Being circular, suggests canvas the more likely.
I can’t guarantee that either method would work – but is it even a strap buckle anyway?
Really the only way is to find the patent, or perhaps ask on a forum dedicated to vehicle preservation.