Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 53-81991 found under Punch And Die Lightening Hole by U S Air Tool Co Inc. The National Stock Number assigned to this part is 3456014282369, and the Federal Supply Class is 3456 Cutting And Forming Tools For Secondary Metalworking Machinery. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 53-81991.