Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number T21-S-767-D-4 1 2 found under Thermometer Self Indicating Bime by Sycon Corp. The National Stock Number assigned to this part is 6685013871142, and the Federal Supply Class is . Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like T21-S-767-D-4 1 2.