The Flexispeed Meteor/ Norfolk had a 1/2" x 16tpi spindle nose. The Perris of the Norfolk era used 1/2" x 20 UNF and Unimat, which the best range of accessories for this size of lathe, used a metric thread which was later increased to 14mm x 1p. Cowell adopted the 14mm thread. I made a mini backplate to fit Unimat accessories to my Flexispeed. A photo of an end mill holder is attached. This might be the answer to the query raised recently.