Abstract: A rotary displacement transducer comprises a shaft rotatably supported in a housing, and to which the rotary displacement to be sensed is applied. The shaft is axially fixed in the housing, and has a precision screw thread formed over part of its length. An internally threaded sleeve coaxially surrounds the shaft in threaded engagement with the precision screw thread, the sleeve carrying a collar having two diametrically opposed radial projections. The first projection carries a roller which engages in a slot in the housing to prevent the collar and sleeve rotating as the shaft is rotated, so that rotation of the shaft causes the sleeve and collar to move axially of the shaft by an amount dependent on the rotary displacement to be sensed. The axial movement of the collar is sensed by a linear displacement transducer of the LVDT type coupled to the other radial projection on the collar.