Final answer:
The provided materials and steps seem to describe a physics experiment, not the process of threading iron pipe. For threading iron pipe, separate steps involving pipe preparation, cutting threads, and cleaning are necessary.
Step-by-step explanation:
The processes provided in the question do not directly explain steps for threading iron pipe; instead, they seem to describe a physics experiment involving a length of plastic pipe and a marble. However, to answer a question related to threading iron pipe, we would need to discuss the steps for preparing the pipe, cutting threads, and ensuring a proper fit for connections. In general, threading iron pipe involves securing the pipe, using a die to cut threads, and cleaning the threaded area. Unfortunately, the given information about an experiment with plastic pipe and a marble is not relevant to threading iron pipe, which is a typically part of plumbing or metalworking.