I was given an old bike and have started to completely disable it. After removing the rear wheel I noticed the hub flanges looked quite different than a normal hub. Instead of a single hole there is a hole large enough to allow the spoke head to pass through and there are slots on each side where two spoke heads are held. Here is a drawing I made to illustrate what each spoke anchor point looks like.

It's very obvious this allows any spoke to be replaced without the need to remove the freewheel. I find myself wanting to put this hub on my touring bike! Anyone else ever seen anything like this?

I know someone is going to want a picture. My camera is not so good at taking close-up photos of rather small objects but here goes.

I have already removed the old and stuck freewheel if your wondering why it's missing.

Does it look like any of these?:
https://www.blackbirdsf.org/maxicar/

what year..more particulars, was it a 7-speed, Shimano..??..??

Yes, on Sturmey Archer hubs where there is a generator.

As Avenan alludes to in his link, this "keyholing" was used on the hubs (usualy Maxi-Car) on French randonneuring bikes in years past. I know that some Alex Singers featured these hubs, and I believe they were also seen on the bikes of Rene Herse.

I would think that this treatment would weaken the flanges and lead to increased failures, but I have no experience with them whatsoever.

That shape was so you could get a spoke out without taking off the freewheel.

Fascinating. And I would never have known about it if I hadn't read the opening post.

The only information stamped on the hub is 4130. I'm 100% sure this is the type of steel used for the hub. Being made of 4130 steel would make this hub near indestructible. It had a very old 5-speed Shimano freewheel. I had to take the wheel to a bike shop that’s been around forever to get it taken off. My LBS did not have the tool to remove it and neither did I. The mechanic told me that tool might not be available for sale anyway. It looks like a standard Shimano freewheel tool would fit except the hole in the freewheel is too small for it to fit. I had to remove the axel before the bike shop could get there tool into the freewheel to remove it.

biketools has the remover for those old small-bore Shimano freewheels.
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True. This was often done just on the drive side, and was a short-lived evolutionary dead end.

This one is done on both flanges.

I've made up my mind to use this hub on my touring bike. This will eliminate needing to haul tools required to remove the cassette on my current hub. The current hubs weight is less than this steel hub but the weight savings considering the tools required to remove the cassette will offset the slightly higher weight of the steel hub. I will not need to remove the freewheel to change out broken spokes. I am going to order a new rim, spokes, QR axel and spacers so I can use it with 130mm dropout spacing and 7-speed freewheel.