4mm double oblique, vacuum hollow glass stopcocks plug with precision ground. With a separate hole in the plug to to create a vacuum in a low vacuum camber.

With solid glass plug. Barrel and plug are precision ground, hand lapped with corresponding numbers on the barrel and plug. With constant pressure retention spring and clip.

Precision ground with corresponding numbers on the barrel and plug Lower vacuum chamber is evacuated via a separate 2mm hole in the plug which is not in the line of flow