In a number of practical situations it is desirable to provide consistency with regard to a metering material presentation. For example, with regard to welding and shape metal deposition it is desirable to provide a homogenous vortex free cloud of gas shielding about a work piece prior to and subsequent to processing. Unfortunately, metering meshes are subject to distortion through thermal gradients. By providing a support matrix arrangement comprising a first planar member and a second planar member incorporating ribbon elements and deflector portions bilateral deflection in the plane of the metering mesh can be accommodated whilst outward buckling is avoided. In such circumstances there is consistency with regard to metering mesh presentation and therefore gas flow through shielding.