A mid-twentieth century beam compass. The four foot beam is in five, eight inch, aluminium sections. Both trammel heads are adjustable by a similar wheel and spring arrangement to that in one of the Norton & Gregory fittings below. A set of similar but larger fittings can be seen in the Harling page as well as a later version of this type.
W H Harling made this pattern of beam compass, which they called the “Roller Pattern Portable Beam Compass” and it is possible that they made this set.