This is the seal to mount the petcock to the tank. It goes around the filter and between the petcock base and the tank. Shown as # 8 in reference picture. Honda part #16958-KM9-005

Some applications include:

CBR600F 87-00
VT600 88-07
VT750 98-09
VTR250 88-90
ZB5 88-
CB400F 89-90
VF750 94-03
VT1100 95-07'
VTX1300 03-09
GL1500 97-03'
CB600F 04-06

PLEASE READ AND UNDERSTAND DETAILS AND PAYMENT/SHIPPING TERMS BEFORE BUYING. THANKS.