NGK CMR7H spark plug. 10mm thread, 1/2" reach, 5/8" hex, gasket seat, resistor plug.
The gap suggested 0.029 inches
 
Zenoah part # 3699-91867
HPI Part # 15454 or 3066
FG part # 07343/08

Stock part on
Zenoah G230RC G260RC G240RC G270RC G290RC G320RC Motors Zenoah 231and 260 PUH and PUM Motors

Can be used on
CY23  CY26  CY27  CY29  GP290
GP460, or any other R/C style motor with same thread size on cylinder for plug