The addition of chromed bonnet studs on either side of the hinge allows the bonnet to be opened and rested fully back onto the other side without damaging paintwork (but must exert pressure on the flat plane of the bonnet top).
The varied locating dimensions of those found suggests that they might be aftermarket or dealer fitments.
Do you have information to the contrary?
If you have these fitted, could you provide the distances from centre hinge and from edge of bonnet panel, to see if there is any consistency in the measurements.
6 inches in from front and rear of panel
3 inches in from centre line at front
4 inches in from centre line at rear
Nick B’s studs as fitted to the dull red ’65’ bonnet in the images above: