Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number US4994 found under Cap Assembly Protective Muffler by Caterpillar Inc. The National Stock Number assigned to this part is 2990004381551, and the Federal Supply Class is 2990 Miscellaneous Engine Accessories Nonaircraft. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like US4994.