I agree, the cranking handle part is able to thread it's way all the way along that larger thread. Both the large and small adaptors look as if they can be swapped out for other sizes.
Yes it looks like a variant of a Churchill 18G 574B BMC cone compressor . I still have one here somewhere.
I did make one but rod must have been a bit soft and the 1/2nf thread stripped under full compression of the cone and frightened the life out of me so picked up the official tool
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local