The inserter/extractors in the Calmark/Birtcher portfolio range from economical type 6 nylon to high performance 6061-T6 aluminum alloy, and are specifically designed for either sheet metal or cold wall applications. They come in a wide variety of designs, each with specific leverage ratios. The design engineer will know the insertion and extractor force needed for their application, as well as the maximum exertion force they want to obtain. From this, the mechanical advantage can be calculated. For example, a board requiring 50 lbs of extraction force, with a maximum exertion force of 10 lbs will require a 5:1 assistance. As previously mentioned, two extractors/inserters are recommended per board. Therefore, in this example, each will need to provide at least 2.5:1 mechanical advantage to disengage the PCB.