An electromechanical actuator for use in a hydraulic braking circuit of a vehicle comprising: an electric motor having a stator and a rotor, and a linear actuator that is located within the motor, in which: the stator is located within a housing having a first end and a second end, the rotor is located inside the housing and comprises an elongate rotor body having a bore passing from one end of the body to the other, the bore being enlarged over a first portion of the body located towards the first end of the motor, and being of reduced size over a second portion of the body located towards the second end of the motor, the linear actuator comprising an elongate shaft that is located within the bore in the elongate rotor body, the shaft having a screw part at one end carrying an external thread that extends along a portion of the shaft that is located within the enlarged portion of the bore in the rotor body, and a fixing part at the other end shaft that is a tightly located into the bore of the second portion of the elongate body to prevent radial movement of the shaft relative to the elongate body, the linear actuator further comprising a drive nut that surrounds the screw part of the shaft and is located at least in a retracted position inside the enlarged bore of the first portion of the rotor body, the drive nut having an internal thread and being connected to the screw part through a set of balls that engage the threads (21, 22) of the drive nut and screw part, and in which the fixing part of the shaft includes a tapering portion that engages a complimentary tapering portion of the bore in the second portion of the rotor body, characterised in that the rotor body is secured to the housing through a bearing race assembly of the kind having an annular inner race that is secured to the second portion of the rotor body, an annular outer bearing race that is secured to the housing, and a plurality of bearings located between the races (12, 13) and whereby the portion of the shaft that extends through the reduced width section of bore in the rotor is provided with an external thread, and further comprising a locking nut that has an internal thread that engages the external thread, the locking nut being sized so that, when located on the thread of the shaft, the locking nut engages both the rotor and the inner bearing race whereby, as the locking nut is tightened, the shaft is pulled into engagement with the bore of the rotor towards the first end of the motor housing and, at the same time, the inner race of the bearing assembly is pressed by the locking nut onto the rotor in a direction towards the second end of the housing. the stator is located within a housing having a first end and a second end, the rotor is located inside the housing and comprises an elongate rotor body having a bore passing from one end of the body to the other, the bore being enlarged over a first portion of the body located towards the first end of the motor, and being of reduced size over a second portion of the body located towards the second end of the motor, the linear actuator comprising an elongate shaft that is located within the bore in the elongate rotor body, the shaft having a screw part at one end carrying an external thread that extends along a portion of the shaft that is located within the enlarged portion of the bore in the rotor body, and a fixing part at the other end shaft that is a tightly located into the bore of the second portion of the elongate body to prevent radial movement of the shaft relative to the elongate body, the linear actuator further comprising a drive nut that surrounds the screw part of the shaft and is located at least in a retracted position inside the enlarged bore of the first portion of the rotor body, the drive nut having an internal thread and being connected to the screw part through a set of balls that engage the threads (21, 22) of the drive nut and screw part, and in which the fixing part of the shaft includes a tapering portion that engages a complimentary tapering portion of the bore in the second portion of the rotor body, characterised in that the rotor body is secured to the housing through a bearing race assembly of the kind having an annular inner race that is secured to the second portion of the rotor body, an annular outer bearing race that is secured to the housing, and a plurality of bearings located between the races (12, 13) and whereby the portion of the shaft that extends through the reduced width section of bore in the rotor is provided with an external thread, and further comprising a locking nut that has an internal thread that engages the external thread, the locking nut being sized so that, when located on the thread of the shaft, the locking nut engages both the rotor and the inner bearing race whereby, as the locking nut is tightened, the shaft is pulled into engagement with the bore of the rotor towards the first end of the motor housing and, at the same time, the inner race of the bearing assembly is pressed by the locking nut onto the rotor in a direction towards the second end of the housing.