There are 2 sizes of pinion flange nuts, 27 spline and the larger 29 spline

If you have a 2001 and Older Toyota Pickup then most likely your pinion flange is going to be 27 Spline unless it has been upgraded.   The easiest way to verify this is to count the splines on the pinion gear. If you want to run the new 29 Spline Ring and Pinions, you will need a new 29 Spline Pinion Flange, Seal and Nut. This is just the NUT, seal and flange are available elsewhere.