that with a given piece of screening machinery different screening operations can be achieved through easy replacement of screen sections as will be seen from the drawing of fig1 access to the interior of the housing 13 is readily afforded by removal of the end plate 13a through removal of the bolts 13b this permits withdrawal of the screen assembly for ready exchange or replacement of the screen sections the thin material of the screen sections may be stainless steel or similar sheet metal which is formed in a generally cylindrical shape having undulations extending around the circumference of the screen in a simplified form the undulations shown in fig5 may take the form of a series of upright and inverted u shaped sections 27a and 27b or in other words the screen essentially consists of a series of deep corrugations these corrugations may be modified as illustrated in fig6 by a shaping of the u shaped sections and as illustrated in fig6 the u shaped section may be formed so that one sidewall 28a of the u is a straight substantially radial wall whereas the other wall 28b has lower and upper straight portions 28c and 28d joined by a circumferential flat wall portion 28e the flat wall portion may perform an additional filtering or screening function and may include the same or different perforations than the remainder of the screen the flat part circumferential portion also adds circumferential rib strength to the overall screen in the arrangement of fig7 the undulations take.