These binoculars were used in danish centururion tanks untill about 1990.
They are mounted in an iron frame weighting about 20 pounds (10kilo)
The frame went all around the middle of the binoculars.
The frame is sliding into place in the turrets ( as far as I know)
I bought 50 of them many years ago, when the tanks were scrapped.
I immediately disposed of all the iron frames, figuring no-one wanted them anyway.
Mine came from a lot of about 250, that had been stoed outdoors. Some of them had nice water levels inside, when you tried to look through them.
Cleaning, and drying, turned out to be easy.
How many were stored in total, I never knew. But for the danish Centurions it was many more than 250.
Some had been repainted at depots. Not always nicely done, and some even had black camouflage in accordance with the late danish NATO army camouflage schemes.
A few came in what I saw as an english olive green colour, indication english use as well.
For photos of use, check google for interiors of centurion tank turrets.