is eventually formed and the two ends of the combined cylinder are joined to the weld rings also by welding although the embodiment provides for a well screen which is made up of parts as described in the figures other embodiments are envisaged for example instead of a metal mesh forming the outer standoff layer 14 it can be another material which provides sustainable a gap between the protective cover 15 and the filter medium 13 such as a strong polymer which may be wrapped around the pipe in a similar way to that described and secured by any suitable means such as adhesive instead of a flat welded mesh other structures may be employed which maintain a gap between the protective cover and the filter medium for example two sheets having a plurality of openings the sheets sandwiching a plurality of spacing pillars or a single sheet having a plurality of radial projections disposed between openings may be employed in both cases the pillars projections being disposed on connected islands between the openings of each sheet alternatively parallel rods spread around the circumference of the filter medium and welded along the length of the filter medium 13 or a series of rings spread and tightened over or welded to the filter medium 13 or a thick metal thread running helically and tightly around the circumference and along the length of.