A series of hermetically sealed glass-ceramic circular connectors offers high density and high-temperature capabilities for use in extreme environments. The headers have up to 41 gold-plated pins and a standard plug on the air side. Three design options are available on the vacuum side for complete versatility: a double-ended design with a threaded plug connection; a straight-pin design with 0.040" diameter pins; and a solder-pin design with solder-cup terminations. The connectors have 304 stainless-steel shells and are UHV-compatible with a minimum leakage rate of 1 x 10-9 standard cc/s of He. Temperature rating is -269°C to 400°C.