A turbine engine defines an axial direction and a radial direction and includes a shaft assembly, a fan or propeller assembly, an engine core, a coupling shaft, a spacer, a sleeve, and a nut The coupling shaft defines an annular surface extended along the axial direction and a groove extended in a circumferential direction. The spacer defines a first portion disposed in the groove of the coupling shaft. The sleeve defines a threaded portion that extends along the axial direction and is disposed outward of the spacer in the radial direction. The nut defines a plurality of nut threads configured to mate with the plurality of sleeve threads of the sleeve. The nut defines a radial portion adjacent to at least a portion of the sleeve and at least a portion of the spacer in the axial direction.