Abstract: A clamp for securing a transducer to a train rail comprises a bracket having a base which engages the foot of the rail. An upright arm at one end of the base extends adjacent the web of the rail and carries a threaded adjuster which engages the transducer and urges it into contact with the rail. The clamp is sufficiently resilient so that, when the adjuster is tightened to a predetermined extent, both temporary and permanent de formation of the rail can be accommodated without difficulty.