www.sparkplugs.com..
r10 865 is not a good Bosch number, look elsewhere on the plug...WSR6F is a Bosch number
Southwest Diesel in Phoenix is a Bosch distributor
If it's a 10mm thread plug there are 3 resistor plugs, Champion, NGK, and Denso...Zenoah G23 and G26 engines use the Champions and NGKs with rubber boots...They work without interference on RC models....The Denso plugs are about 3/8" longers....All three can be ordered from sparkplugs.com....Don't go to Horizon, they charge about double....

I tried to go to sparkplugs.com from the link at the top, I guess Marc doesn't like advertising..
Type it in your browser search engine