I'm curious about square bridges on Mausers. I've never seen one in person and you can tell I don't know anything about them.

In looking at archive photos, it appears to me that receivers with a single square bridge do not have a charger hump, is that correct? Do single square bridges have a standard height - might they be the same height as the ring? Are the square bridges there just for looks, or are they there for some function (I know that claw mounts were mounted on some, but in many photos I've seen, the top surface is just checkered or grooved)? Was there any rhyme or reason why some Mausers have double square bridges, some have a single square bridge on the bridge, and some have a square 'bridge' on the ring? Did all Magnum Mausers have them, or just some Magnums? Do some standard size Mausers have them as well?

Any enlightenment would be much appreciated.