Jacketed fractionation distilling head for use under vacuum. The 10/18 top outer joint is for a 1” immersion thermometer while the 10/30 joints are for a 2” immersion thermometer. The 24/40 joint size uses 4mm glass or PTFE stopcocks, and are positioned to permit changing of receiver without interruption of the distillation process. The 14/20 size uses 2mm bore glass or PTFE stopcocks.