I've just nipped out to the garage to check. It's not there so I think it must be in the barn. I'll try to get over there and measure it in the next week.
Where about are you located?
Getting the arm off can be a bit of a challenge.
I have a 10 Tonne hydraulic puller that eventually got the job done. I have lent it to others to remove their drop arm.
TBH I'm not sure what connection you mean?
I just know that annealing the copper softens it so it can deform to make the seal.
There are loads of far more knowledgeable people on here than me.
What engine do you have?