Screw taps are used to create the inner cutting edge.
Tommy Bars are used to untwist fasteners, cutting locksmith tools. Also used as holders and retainers for socket heads, various extensions or additional attachments for parts, etc.
Dies help create and calibrate threads on the outside of the item part. Dies have cutting edges on the inside and can be used in inaccessible places due to their compact size. They are widely used in engineering structures such as pipelines.