ONLY use on 64 Pitch Spur Gear For replace PN Racing MR2044 or MR2045 Ball Diff Download Printing Size 2WD Gear Ratio Chat Modifying the Kyosho diff to fit the PN Ball Bearing Spur Gears. Pic 1 & 2: The inner hub of the diff extends slightly outward from the diff ring. With the new gears that bump gets in the way and will not let the gear sit flush with the diff ring. Pic 3 : Use some 400 grit sand paper. Pic 4: Lay the paper on a flat surface then in a circular motion sand down the hub. Keep checking the hub and stop when it sits flush with the diff ring. Pic 5 6 & 7: Here is the sanded down diff now sanded down enough for the PN gears. Pic 8: Here is the Diff with the gear installed before the outer hub goes on. Pic 9: This is the Kyosho Diff with the new PN Ball Bearing Spur Gear installed. This was very easy to do and only took about 15 minutes to complete.