This is the Kyosho spur gear:
http://www.rc-monster.com/proddetail...YOIF148&cat=40
You can use the 5mm bore mod1 gears that Mike sells. Just a guess, a 14t pinion might do well.
SH Z-Car, Custom Crawler, 8s Savage,
12s XTM XLB 1/7 buggy,
4wd 4-link rear/IFS Pro4 truck,
Custom Hyper 10 Short Course,
Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz