Helical spur gear, you wont find a pinion to fit that unless you get a custom made one from https://sdp-si.com/eStore/ , and I dont see anything quite suitable there either actually. Your best bet would be to ditch that spur and find a normal one to replace it...
thanks for the help but i replaced it with a centre diff from a x1 crt 51 tooth , i have a medusa 70mm 2300kv should i gear it for 41 mph or 45 mph ???
On 4s lipo? 41mph would be good, but experimentation is the key to good temps and performance- try different pinion combos until you fin the one that works best for you (cool motor/esc/lipo temps + enough speed for what you are wanting to do).