Unrecognized part 1972 Commando Combat

Can you help identify a part on a 1972 Commando Combat.
This bike is new to me. It has an incomplete history but there is documentary evidence of an engine rebuild back in the late 1970's.

I cannot find any reference to the unit indicated by the red arrows in the following pictures.

Any ideas?

crankcase breather, the hose connected to the top of it goes to the oil tank

Crankcase breather (1972 specific). There are numerous threads on what needs doing to upgrade this and recommendations to fit PCV valves (I use a Yamaha yzf125 one).

Cheers
Graham

https://andover-norton.co.uk/en/shop-dr ... eter-drive
Item 46.

nortonmews said:

Crankcase breather (1972 specific).

Click to expand...

Also 1973 750 models.