It is only a short piece of pipe (about 25mm or 1" long, and perhaps
10mm or 3/8" outside diameter), and the ends are open, with the wires coming out. I then put it inside some heatshrink and sealed the ends with that to stop air flow through the pipe. Basically I needed to put the little dead-bug board in something to protect it mechanically, and the copper pipe had the added bonus of keeping it fairly isothermal. I was afraid that there might be some high thermoelectric coefficients between the resistive material in the resistors and the end contacts, or perhaps between the bond wires and chip pins etc. so I wanted to try to get rid of thermal gradients. I used thin magnet wire for the input connections and taped it to the copper pipe (before putting the heatshrink over everything) so that not much heat should reach the solder joints on the board via those wires. Probably overkill.Chris