This depends on many factors. SPI guidelines suggest .0015” (.04 mm) per inch of screw diameter starting clearance between screw and barrel. For a 50 mm screw this is .003” (.08 mm) clearance per side or .006” (.13 mm) overall. Depending on resin viscosity, output can be reduced 25% with a doubling of this beginning clearance (.012”, .25 mm). The effect screw wear has on production and part quality should be an important consideration. An extrusion system can be especially sensitive to adhesive wear of the feedscrew outside diameter.