They're 50 ohm RF and DC feedthrus. Here's the company:
http://www.shp-seals.com/products_and_Services.htm
Click on bulletin 100. Most50 ohm types gave a VSWR of 1.05ish, giving
about 53 ( or 47 ) ohms. I also had a few of the DC type that gave a
VSWR of 1.4ish, leading to about 25 ohms ( or 75 ohms, could I check
the phase to see which?).