Abstract: A bore screen for use in filtering fluids which are extracted from bores or wells and which comprises a stack of annular plastics material rings which are clamped together in face-to-face relationship. Each ring is formed on opposite, first and second, faces with aligned, circumferentially spaced bearing pads, the bearing pads on the first face of successive rings contacting those on the second face of adjacent rings and serving to space the rings apart. The bearing pads on the first face of each ring are formed with stepped projections and those which are on the second face of each ring are formed with complementary stepped recesses, and the bearing pads mate in such a way that the spacing between adjacent rings is changed as one ring is rotated relative to another and different pairs of bearing pads are brought into contact with one another.