This differential is for 2015-2020 F150s with a Super 8.8" rear end. Spline count is not helpful in this situation, since both the 9.75" and Super 8.8" have 34-spline axles and 12 cover bolts. The easiest way to tell the difference is visually. The 9.75" rear end is tapered to the passenger's side. The Super 8.8" is symmetrical. If you need assistance with figuring out your F150's rear end, give us a call directly at 623-434-5277.