Solid glass high vacuum stopcock with theChemglass improved constant pressure retention device. This retaining system incorporates a glass plug having an extended snelling which accepts a stainless steel spring and clip. The spring keeps constant tension on the plug at all times and is easily removed and attached. Plug is precision ground and hand-lapped with corresponding numbers on the barrel and plug. Each stopcock is supplied complete with a stainless steel spring and clip. Replacement retention kit consists of one spring and clip for the plug size listed.