A driveshaft assembly includes a driveshaft with a shaft axis, a first end, and a radially outer surface. The first end includes a plurality of recesses extending radially inward from the radially outer surface and each including an engagement surface. The driveshaft assembly also includes an end housing with a receptacle including a plurality of planar receptacle surfaces. Further, the driveshaft assembly includes a torque transfer assembly including a plurality of torque transfer keys each with a planar key surface and a convex key surface, and an adapter including a plurality of concave adapter surfaces and a plurality of planar adapter surfaces. The engagement surface of the each recess engages the planar key surface of one of the keys. The convex key surface of each key engages one of the concave adapter surfaces. Each of the planar adapter surfaces of the adapter engage with one of the receptacle surfaces.