Imperial threads

Imperial threads are designated not by their pitch but by the number of threads per inch (tp.L). The leadscrew of a metric centre lathe has a pitch of 6mm and, since the number of t.p.i. cannot be arranged as a multiple of the leadscrew pitch, the split nut, once it is engaged, must never be disengaged during the thread-cutting operation. This also means that the thread indicator dial is of no use when cutting imperial threads on a metric lathe. 

The procedure when cutting imperial threads on a metric lathe is the same as before up to the point when the split nut is disengaged and a trial cut taken. 

Some larger components are fitted with a drilled and tapped hole to accept an eyebolt to simplify lifting. Collar eyebolts, manufactured to BS4278 1984 are available with threads from 6 to 52mm with larger sizes available to order. Imperial threads are available for replacement on older equipment. Typical SWL of an eyebolt having an M45 thread is 8 tonnes. 

John Dee wove together the threads of British Imperial Christianity from Trojan and Arthurian legends and the Hebrew Kabbalah into the Elizabethan Rosicmcianism. 

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