Abstract: An electric submersible pump (ESP) assembly that includes an electric motor with a splined drive shaft with drive shaft teeth, an ESP mechanically coupled to the electric motor that includes a splined ESP shaft with ESP shaft teeth, and a downhole component mechanically coupled to the electric motor that includes a splined component shaft with component shaft teeth. Splined couplings each include a central axis and grooves through the coupling with groove sidewalls sized to receive the shaft teeth. The grooves are angled relative to the central axis to form a space on either side of each tooth in each groove for at least a portion of the overlapped length of the tooth within the groove. Each coupling is engageable with the teeth of two of the drive shaft, the pump shaft, or the component shaft to mechanically couple the electric motor, the ESP, and the downhole component.