What collet is a 4C? Is the collet marked 40 and is the hole 4.0 mm? The lathe is not an A, 750 or Elect model. From the picture, I can tell it is either an 8 mm or a 10 mm with 50 mm center height. You say it is not 10 mm, so that leaves 8 mm for the collet body diameter. But Derbyshire made two kinds of 8 mm collets, either of which will fit the lathe. The difference is the thread size of the collet and, of course, the thread size in the draw bar. The markings or absence of markings near the headstock serial number are a clue to the model. His early 8 mm lathes were Webster-Whitcomb model, but he stopped stamping that name once he enlarged the headstock spindle to allow using either the WW or the Large collets. The word "Hard" stamped by the serial number means the bearings are hardened steel, not babbitt or ball bearings.
The tailstock was not made by Derbyshire, but there were several lathe makers that made that style of tailstock, so I can't say who made it.
The basic lathe design is based upon the American Watch Tool Co. Webster-Whitcomb model. Derbyshire first worked for AWT before starting his own factory, and later bought the rights to the AWT lathes and trademarks. He improved the WW design to allow his 8 mm "Large" collet, with a larger thread for increased through capacity. Many other companies copied the WW design (lathes and collets), which is why a tailstock from a different maker can more or less fit a Derbyshire lathe with 50 mm center height.
By the way, the A and 750 models have a 75 mm center height and the Elect has a 60 mm center height. The Magnus model has a 50 mm center height, but takes 10 mm collets.
Larry
