Équivalences 
http://www.sparkplugs.co.uk/index.htm :
Alternative spark plugs for NGK BPR8ES:
Details about NGK BPR8ES:
    Threaddiameter: 14mm
    Threadreach: 19mm
    Seattype: flat
    Hexsize: 21mm
    Tipconfiguration: projected
    Construction: Standard construction
    Terminaltype: Removable
Possible spark plugs:
    AC Delco 41XL
    AC Delco R41XLS
    Accel 112
    Autolite 4251
    Autolite 4053
    Autolite 51
    Beck Arnley 176-5086
    Bosch WR5DC
    Bosch W4CC
    Bosch WR5DC+
    Bosch stk 7530
    Brisk LR12YC
    Brisk LR12ZC
    Champion OE116/T10
    Champion RN6Y
    Champion N6YC
    Champion OE116
    Champion RN4YC
    Champion RN6YC
    Champion N2C
    Champion stk 904
    Champion stk 315
    Champion stk 805
    Denso W24EPR-U
    Denso IW24
    Denso W24EPRU
    Denso W24EPR
    Denso stk 4136
    General Motors 5613161
    General Motors 5614070
    Honda 98079-58847
    Iskra FE95CPR
    Kawasaki E92070-1044
    Motorcraft AGR12
    NGK stk 3923
    PAL (Brisk) LR12YC
    Splitfire SF6A
    Yamaha 94700-00219
    Yamaha 94701 00219
    Yamaha 90793-20062
    Yamaha 94701-00219