The most commonly used type of general-purpose screw thread, one of the first international standards agreed when the International Organization for Standardization was set up in 1947. Metric threads are becoming more common in model engineering, but there are quite a few applications where other, perhaps better scale threads are still used – see our Threads page for a list of the other forms.
BS 919-3:2007 Screw gauge limits and tolerances. Specification for gauges for screw threads of ISO metric form
ISO 68-1: ISO general purpose screw threads – Basic profile – Metric screw threads.
ISO 261, titled ISO general purpose metric screw threads-General plan, is an international standard that defines a detailed list of preferred combinations of outer diameter D and pitch P for ISO metric screw threads.
ISO 262, titled ISO general purpose metric screw threads-Selected sizes for screws, bolts and nuts, defines a shorter list of thread dimensions – a subset of the combinations listed in ISO 261