Processors should at least understand what type of screw and what the key numbers are for the screw in the machine of choice. Decisions can be made about whether the screw is suitable for the material to be molded. Keep in mind that the term “GP” is a relative term and one “GP” screw is not necessarily the same as another.When pulling a screw look for hang up areas and locations of carbon buildup on the screw. These will indicate potential areas that will lead to brown streaking (or black specks and splay). See Figure 17.6 for an example of a screw with severe buildup that was leading to molding problems.