The correct term is "Clip Mount" They used two different hole spacing over the years. Every Granitone, three ply and earlier example that I have seen has the narrow spacing and two screws at 12 and 6 o clock.

The later ones, from very late 70's into the 80's used a wider spacing that was the same as the Classic L arm mount. On those later drums, the holes may or may not need to be enlarged for the bosses on the mount to fit into. If you have earlier drums with the narrow spacing you would either have to drill new holes or fashion some sort of adapter plate.

They started using four screws when they went to the wider spacing. Two at 12 and 6 o clock that hold the clip mount on and two at 3 and 9 o clock to hold the mounting plates. This was probably due to to the heavier weight of the 6 ply shells and power toms that were becoming popular during that time frame.

Thanks for the info and the correction. I have called them bayonet for years but will correct that error. These are a Cortex, Octaplus kit from 1976. Based on the year, is it safe to assume they have the narrow spacing?

Most likely the narrow spacing.

They made three types of mounts. Two small and one large. This makes them pretty easy to spot.

The smaller ones had 1-1/4" spacing

These are the top two on the left picture and the first and second from left to right after that picture.

The larger one had 1-7/8" spacing. They also had an extra set of holes with the older spacing to make the new mounts backward compatible with older drums.

This is the third picture. You can see that is is a good bit bigger than the older ones. The clip is also smaller than the backing plate and the backing plate has the two extra screws to the sides.

Also note that the older mount has the clip mounted very close to the backing plate. The middle and later versions space the clip out about a 1/4".

This means that the drums with the oldest mount will be a little closer together and the stand will have a smaller diameter felt ring. The later stands had a larger felt or rubber ring.

If you don't want to modify the drum, the Inde BR2 mounts have adjustable hole spacing that will work with either version of drums you have. They will also accept any size L arm so that is a plus.

https://www.indedrum.com/drum-upgrades-accessories/inde-suspension-mounting-bracket

Thank you @thin shell. Much appreciated.

thin shell pretty much has it spot on.

I will add that they are referred to as Ludwig Hercules series mounts with 1" tubing.

These are the ones you are referring to.

The Ludwig Atlas series mounts have the L arm mounting system.

What's great about the Hercules is that it's modular, and you can use their boom stands to mount the clip shaft and essentially have boom tom stands for large kits, if that makes sense.

(I wouldn't do it for larger toms, primarily the small ones that would sit over hi hat).

When I had my 6" and 8" concert toms (melodic sizes) built from RCI, I did inquire to Romano if I could pick up some more clip mounts and where were they, and if they still were available.

He told me that Ludwig actually 'lost' the die set and plans for these mounts so they (Ludwig) have no way of recreating these clip mounts.

I am not sure if it's accurate, but I figure Romano knows as he sources his shells to different manufacturers, or it could be Ludwig not wanting to sell the proprietary plans.

Thanks for that. I wasn't aware of these as an aftermarket arrangement. I love the algorithm leading to, "Want your drum to sound awesome? - no, go buy something else". Laughing H