Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number NSTDSIZES21L found under Heater Ventilation Duct Type by Modine Mfg Co. The National Stock Number assigned to this part is 4520002731060, 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 NSTDSIZES21L.