Abstract: A self-locking adjustable support device comprising two telescopically interfitting members, a housing and a means for connecting the housing to one of the telescopically interfitting members in a manner permitting the housing to be adjusted in position longitudinally relative to one member. The housing is formed with a portion having an internal frusto-conical surface arranged to receive a plurality of locking elements which can be jammed between the frusto-conical surface and the outer surface of the said one member to inhibit movement of said other member in one direction longitudinally relative to said one member. The connecting means is a screwthreaded member which permits rotation of the housing relative to one member to afford fine adjustment of the overall length of the support device.