Fuel pickup and reserve unit

[Thomas591]

My 411 S5 was suffering from the strange problem that shortly after the fuel gauge showed half tank, the motor stalled. When the reserve switch was on, the motor continued for another 10 km and then ran out of fuel.

I replaced the fuel pump with a stronger unit: no change.

I checked the fuel gauge and sender unit: everything fine here.

Finally it dawned on me that the fuel pick up might be the problem. So today I took the unit out of the tank and a close inspection showed that the brass pick up tubes were full of hairline cracks.

I cleaned the brass tubes and soldered up all the cracks. Normally the brass tubes can be replaced fairly easily as they have 7mm outer diameter, but I was not able to identify the thread on the end of the brass tube that threads into the mazak top.

Question: which thread size was used by Lucas for a 7mm tube ( the thread has 26tpi)?

For reference purposes: The Lucas number for my pick up is 78037B and the Lucas catalog states a length of 9 35/64 for the main tube and 11 51/64 for the reserve tube.