Oil baths heated by Instatherm reg;, an integral noble metal alloy fused permanently to the glass & covered with a tough silicone rubber treated glass cloth insulation which serves as a thermal barrier as well as protection against physical shock. Rapid heat response - low thermal lag. For use with all Ace proportional temp controllers to get precise, accurate and safe heating. All baths include a connecting controller cord (9698-20). Codes -38 thru -55 include a thermocouple/thermometer holding clip in addition to the 9698-20 cord.