Nigel, my Flexispeed, which is just about identical to the Norfolk, has a 1/2" BSF thread, and the register, just behind the threaded portion of the spindle, is a very neat .500 diameter. Try measuring that, using a thread gauge or a tap will identify the tpi. If the register is larger, it may be 14mm, which I think may be the Perris/Cowells version. Hugh.