Cap
Materials
Aluminum 6061T6 Rod, 1/2" dia, from AmazonSupply
Rubber O-ring
Electrical Tape * Revision: Not so good. The heat makes the tape go gooey and rub off. Use another substance or just use the bare aluminum
Revision: drilling long holes is difficult. Starting with a tube and capping one end and threading the other end might be better. See TIG Welder Cap