These are some spool clamps I made on  my lathe early on in violin making.  These are maple and roughly follow the specifications laid out in Courtnall.  I made 32 of them.  I modified the design to include a raised area so that the stainless steel threaded rod does not come in contact with the edge of the plates.  The rod is fixed on one end to ease installation.  They are lined with cork with a diameter of about 25mm and have a capacity of 47mm.  The finish is two coats of tung oil.  This jar exactly fits the 32 of them, so that’s where I keep them.  They work well!