this is very similar to Quick ‘n dirty DIY Vacuum Feedthrough – Amateur Nuclear Physics
Ordered in some copper crush washers (#97725A250, M12 Screw Size, 12.2 mm ID, 15.9 mm OD, 1.3-1.7 mm thick) from McMaster. These worked well, though a large amount of torque was required to seat them, and I’m not sure how the aluminum threads are holding up. A substantial amount of black residue was deposited onto the surface of the spark plugs from the last attempts. I am unsure of its composition.
Copper sealing rings worked perfectly.
Ben Krasnow has you spark plugs as well for his SEM, although interestingly he’s flipped them around, with the ceramic on the inside.
Spark plugs apparently use a talcum powder ring for sealing. Very unusual. I’m going to look into this.
In any case, the plug body is typically made of a nickel steel alloy.
my vacuum base plate was about a quarter inch thick. I threaded these
I’ve managed to put 45 amps through these plugs for short periods - worked great.
Glass tubing for spark plug HV insulation
Purchased some NGK D8EA non-resistor gasket copper-core plugs. These have an M12 x 1.25 thread and a 3/4" (19 mm) reach, gasket seat, apparently equivalent to Autolite AR4152, NGK D8EA/2120, or Denso X27EP-U9. Had to cut the gasket seats off.
M12 x 1.25 thread and a 19 mm reach.
Solder wets the tip of these plugs very well if the surface is sanded slightly. broke the tip off