Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number M3991D found under Seal Plain Encased by Lull Corp. The National Stock Number assigned to this part is 5330008524425, and the Federal Supply Class is 5330 Packing And Gasket Materials. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like M3991D.