This method of cutting wooden threads depends on master screws. These are used to establish the pitch of the thread being cut as wooden blanks are guided through a die. Above are my three 1″ diameter master screws and two of the brass nuts that are needed for their use. The bottom screw is a ‘double start’ screw; meaning it has two threads intertwining (a double helix). Even though it looks like the finest of the three it is actually the coarsest at 3 threads per inch (3TPI). Above that is a 4 TPI master screw and at the top a 5 TPI one.
The nuts and screws are easily switched out of the wooden threading frame. The brass nut can be unscrewed from its flange and replaced to substitute a master screw of a different pitch. The black steel part on the right is a shaft coupling; in this case it connects the master screw with a bit brace which is used to drive the screw by hand. You can see this on the video, “Threading a Wooden Screw”.
At the opposite end of the master screw an identical shaft coupling is used to make a connection with the wooden screw blanks. Here is the set up for my smallest (5 TPI) screw blanks which have 1-1/2″ diameter handles. The white plastic part is an adapter which makes the transition from the 1″ inside diameter of the coupling to the 1-1/2″ outside diameter of the screw blank. For other screws this adapter isn’t needed since the outside diameter of the coupling matches that of the screw blank handle (1-3/4″). In all cases a short length of radiator hose and hose clamps are used to securely fasten the wooden blank to the master screw.