Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number HL557 12 20 found under Pin Rivet by Satair A S. The National Stock Number assigned to this part is 5320012882871, and the Federal Supply Class is 5320 Rivets. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like HL557 12 20.