A support assembly for an item of furniture has an elongated support structure with a first pair of feet fast with the support structure at its lower end; a passage defining arrangement defining a guide passage fast with the support structure and extending lengthwise; a support member displaceable with respect to the support structure which has a second pair of feet at its lower end; an elongated a guided pin fast with the displaceable support member that is complementary to and longitudinally slidably engaged with the passage defining arrangement, so that the displaceable support member is slidably displaceable along a rectilinear guide path which is transverse to lines drawn between both the pairs of feet, the passage defining arrangement comprising a hollow carrier with a pair of longitudinally spaced precision washers which engage the guided pin, the dimensions of the washers and the guided pin being such that automatic frictional engagement of the guided pin occurs, in use, with inner walls of the washers in response to pivoting of the displaceable support member about a pivot axis which is transverse to the displaceable support member's guide path, automatically to anchor the displaceable support member frictionally against sliding displacement relative to the support structure.