Double-walled, borosilicate glass, immersion well for use with 7863, 7864, 7865, or 7891 reactors and 7825 lamps only. A small diameter inner tube extends down the annular space to insure flow of coolant from bottom of well upward to outlet. Well is used with 7506-14 nylon bushing with FETFE O-Ring to form a compression type seal with threaded reaction vessels. Well offers a greaseless connection and can be adjusted to desired height. Code -40 for use in 7863, 7864, and 7865, all capacities.