Metric threads

FPN) Some equipment provided with metric threads will need suitable adapters to permit connection to rigid conduit with NPT threads. 

The first stage in tapping is to drill a hole of the correct size. This is known as the tapping size and is normally slightly larger than the root diameter of the thread. Table 2.2 shows the tapping sizes for ISO metric threads which have replaced most threads previously used in Great Britain. 

The thread now standardised in British industry is the ISO metric thread, ISO being the International Organisation for Standardisation. Terminology of this thread is shown in Appendix 1. 

The ISO metric thread has a 60° truncated form, i.e. the thread does not come to a sharp point but has a flat crest. The root of the thread also has a small flat. 

Having turned the workpiece to the correct diameter, the following procedure should be followed. This procedure is for screw-cutting a right-hand external metric thread on a machine having a metric leadscrew. 

Figure 932. Screw-cutting tool for metric thread...

Since 1965, British industry has been urged to adopt the ISO (International Organisation for Standardisation) metric thread as a... 

All components were arranged on a standard optical table, 25 mm grid spacing of 6 mm diameter metric threaded holes, for ease of arrangement. All optical components were mounted in standard steel or aluminium post and bases and using... 

Since 1965, British industry has been urged to adopt the ISO (International Organization for Standardization) metric thread as a first-choice thread system, with the ISO inch (unified) thread as the second choice. The British Standard Whitworth (BSW), British Standard Fine (BSF), and British Association (BA) threads would then become obsolete. The British Standard Pipe (BSP) thread is to be retained. The changeover has been extremely slow in taking place, and all these threads are available and still in use. 

As shown above, optical detection systems can be assembled in a variety of ways. Easily switching between available choices requires standardizing connectors. On the one hand, standard threads for connection to liquid drivers are usually 14-inch, 28 threads/inch, which is the typical format in FIA. On the other hand, standard threads for connection of optical fibers are typically those of SMA 96 (14-inch, 36 threads/inches). Additionally standardizing head threads can greatly facilitate connection of various components. Figure 5.16 shows some accessories with the European metric thread 14 fabricated in our workshop. 

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