MG T-ABC

Does anyone know what size the small screw is that retains the gas tank trigger? Mine is currently held in place with a cotter pin. I am planning to fit a new spring (mine is missing) and would like to install the proper hardware as well.

A cotter pin is correct
https://cdn.shopify.com/s/files/1/0270/ ... 1652107280

The cap is assembled with a split (cotter) pin but the trigger and its spring are secured with a screw. I Haven't checked the thread but the major diameter of mine measures approximately 2.70 mm. Given the era of the TC I would guess the thread to be BA (British Association).
2.70 mm is within a knat's cock of the major diameter of a 6 BA screw (2.79 mm) so I think that's likely to be it.

Doug's re-creation of the gas cap internals is quite a bit different from the original design. Note the much simpler
original "ribbed washer" design and lack of a nut to hold it all together. Looks like Doug's ribbed washer is a smaller diameter and the entire sealing arrangement has been modified. Of course this cap had the cork or paper seal disintegrate long ago. Nickel plating has sure held up well on the ribbed washer.

You have to be careful with the repro seal assembly. The nut tends to unthread and everything falls into the tank. I used some blue locktite on the last one I installed and it seemed to stay put. The one on my car is still original.

Screw to hold the trigger in place is 6BA slotted countersunk, originally brass.
It's a real challenge to get the trigger, spring, and screw all together.
Tom Wilson

Thank you! Looks like Doug Pelton has them in stock as well.

Tom, what I found is to take a toothpick with the point removed and insert it from left to right into the first tab. Now take the trigger and the spring coiled and put it into position. Push the toothpick into the assembly and now insert the screw from the right pushing the toothpick out. It's certainly a pain trying to juggle fingertip small pieces with a spring to scatter it all over but not the worst task.