Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 4N4021 found under Adapter Turbo Oil L by Caterpillar Inc. The National Stock Number assigned to this part is 2990011473004, 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 4N4021.