These are definitely constructed from tough materials, like stainless or carbon metal. Used to connect different elements to concrete. Attempts were being produced inside the early twentieth century to convince the governments from the U.S., United kingdom, and copyright to adopt these international thread specifications along with the metric process https://typesofroofvalley62727.blogs100.com/29836214/little-known-facts-about-types-of-screw-heads-names