The stock 7.5 has 18 degree hubs. The k2 has 22 degree and has different upper arms, the different upper arms are used for 20 and 22 degree hubs. Most people are using 20 degree hubs not the 22. You can purchase the ofna hyper 7 20 degree hubs they are half the price you will just have to purchase the kyosho upper arms and they are the same. Ofna lables them 19 degree but when you look at them they have 20 degree written on them just like the kyosho ones.