An electric brake comprises an actuator module including a module housing, a reciprocating ram, and an electric motor operatively connected to the reciprocating ram for selectively extending and retracting the reciprocating ram with respect to the module housing. The ram has an inner portion of non-circular cross-section and an outer portion of circular cross-sectional, and the housing has a guideway for the ram, which guideway has an inner portion of non-circular cross-section for interacting with the inner portion of the ram to prevent rotation of the inner portion of the ram, and an outer portion of circular cross-sectional. The actuator module can be equipped with a bi-stable holding brake having a first state permitting at least retraction of the ram and a second state preventing at least retraction of the ram.