Hello Blacksmiths, Locksmiths, Clock and Watchmakers, I am quoting from  George Daniels: "Watchmaking" book "Screw Plates The screw plate is not so much used now that standard sized taps and dies are available. For small threads up to 0.6 mm diameter the screw plate offers no advantage, but for larger diameters they are often useful because of their finer thread pitch. A plate is illustrated in Fig 48 and it can bee seen that the thread holes are numbered for association with the