If you need to install internal thread inserts, the Zoro SELECT 5PWY7 Mandrel is your best bet. It has a 5/16-18 coarse thread size and is compatible with the Zoro SELECT 5TUW5 Insert Tool. The threaded insert tool is made from steel for durability. This coarse threaded mandrel measures 5/16″ in diameter and 18 threads per inch. It can be used to install both external and internal thread inserts. When it comes to getting quality tools at affordable prices, you will definitely want to invest in the Zoro SELECT 5PWY7 Mandrel.