The top rollers must be pressed with relatively high force against the lower rollers to ensure guidance of the fibers. Pressures are in the range of 100 to 250 N (300 N) per roller (shaft) and they depend upon raw material and volume. Adjustment may be continuous or in several steps. Today, the required pressure is achieved by springs or by pneumatic means (i.e. Texparts PK 5000). In the past, Platt Saco Lowell also offered a magnetic weighting system.