The screws are BA thread - I replaced the 8 rusty screws that hold the chassis in the box .
The 4 BA C/sunk screws holding the meter cover on were really stuck, some patience needed .
The meter face is now visible ! I have a left over bit of crumpled 1940 plastic lens.
BTW I don't know who thought up the theory of the C tuner . In actual field use , I've heard that all it did was absorb some of the RF energy that was meant to go up the antenna
