On the early KV 1's i sometimes see a cylinderical fuel tank and sometimes see a much narrower cylinderical tank. What is the small tank?

The smaller tank was for oil. There was also a long rectangular box-like oil tank sometimes seen on both KV and T-34 fenders.

Early KV-1 and some KV-2 tanks carried smaller box-like fuel cans on the fenders before the cylindrical models became the standard type. These seem mostly fitted to KV tanks. T-34 sometimes carried a pair of larger box-like fuel tanks on the rear hull plate. These were not seen on KV, to the best I know.

The small KV fuel-"boxes" are available as resin AM bits - very cool and well-done, IMO.

Bob

That's not a tank, it holds the gun cleaning staffs and heads. All of the cylindrical liquid containers on the KV were the same size.

KL

Have to agree with Kurt,

All cylindrical fuel tanks were the same size. The narrow cylinder on the left fender was for gun cleaning rods. Later all tools were moved to the flat rectangular stowage boxes.
Early KV-1's built in Leningrad, had square shaped fuel tanks.

https://www.scalemates.com/nl/kits/panzer-art-re35-146-fuel-drums-soviet-kv-1-2-tanks-early-pattern--223101

Hello!
It is difficult to call these tanks early.
Square fuel tanks were installed on production tanks no earlier than July 1941.
And by October 1941, the production of KV-1 tanks, in Leningrad, was actually stopped.

So.. When did the cylindrical fuel tanks start being used on the KV-1 ?

Did they have fuel lines or were they just storage tanks.

How did they mount to the fender? I have difficulty finding a good photo of the mounting hardware.

Cylindrical fuel tanks were installed in Chelyabinsk.
Installation began in August (roughly) 1941.
The tanks built in Leningrad did not have such tanks.
The fastening of the tanks can be seen in this photo -



In principle, subsequently, this fastening was preserved.
For example, on the SU-152 -



There were no fuel lines