本发明公开了致动器下部附接件，并具体公开了螺杆致动器，其包括：主螺母；具有第一螺纹的第一次螺母；具有第二螺纹的第二次螺母；以及第一附接装置。第一螺母、第一次螺母和第二次螺母以第一次螺母与第二次螺母之间的第一初始轴向间距连接到第一附接装置。第一次螺母通过允许第一次螺母相对于第一附接件旋转的轴承安装到第一附接装置。第一次螺母通过具有小于螺杆致动器轴的螺纹的螺距的螺距的螺纹连接部连接到第二次螺母。当主螺母失效时，第一次螺母和第二次螺母的螺纹抵靠螺杆轴的螺纹负载从而相对于彼此旋转，并且第一次螺母和第二次螺母从两者之间的第一轴向间距移动成不同的第二轴向间距。

A screw actuator having a screw shaft and a nut arrangement is described herein, the nut arrangement comprising: a primary nut (54); a first secondary nut (56) having a first thread (60); a second secondary nut (58) having a second thread (64); and a first attachment means (52). The first nut, first secondary nut, and second secondary nut are connected to the first attachment means with a first, initial, axial spacing between the first and second secondary nuts. The first secondary nut is mounted to the first attachment means via bearings (59) that allow the first secondary nut to rotate relative to the first attachment. The first secondary nut is connected to the second secondary nut via a screw thread connection (66) having a pitch lower than a pitch of a screw thread (62) of the screw actuator shaft. When the primary nut fails under load, the threads (60,64) of the first and second secondary nuts (58,58) load against the screw thread of the screw shaft (102) which causes the first secondary nut to rotate relative to the second secondary nut and, as a result of the screw thread connection (66), the first and second secondary nuts (56,58) move from the first axial spacing between the first and second secondary nuts to a second, different, axial spacing between the first and second secondary nuts. A method of manufacturing this arrangement as well as a method of reducing backlash in such an arrangement is also described herein.