A fillet is a tool for producing a continuous straight line or combination of lines in tooling. It is similar in structure, but larger than, a farthing wheel. A fillet can be used for both blind and gold tooling. It consists of a brass wheel, mounted on a brass shank set into a wooden handle. The rim of the wheel is filed down to produce a line of a given width.


    _____
   /     \                  \
 /         \                |
|     _     |               | brass wheel
|    <o\    |               | approximately
|     \  \  |               | 5 cm / 2 inches in diameter
 \      \  \                |
   \_____/\  \              /
           |  |             \
           |  |             |
           |  |             |
           |  |             | brass shaft
           |  |             | approximately
           |  |             | 10 cm / 4 inches long
           |  |             | 10 mm / 1/2 inch in diameter
           |  |             |
           |  |             |
           |  |             |
           |  |             |
           |  |             |
           |  |             |
           |  |             |
          /____\            /
         |      |           \
         |      |           |
         |      |           | wooden handle
         |      |           | approximately
         |      |           | 30 cm / 12 inches long
         |      |           | 25 mm / 1 inch in diameter
         |      |           |
         |      |           V

As with any tooling, tooling using a fillet is done by heating it up and impressing the design in (usually) leather. A fillet is generally used on the cover of a fine binding, but not the spine.

To end the line created by a fillet, there are three common techniques.

  1. A mitred fillet
    This is a fillet with a slight gap in the rim.
        _____
       /     |       \  mitre
     /        \_     /
    |     _     |
    |    <o\    |
    |     \  \  |
     \      \  \
       \_____/\  \
               |  |
    
    To use a mitred fillet, run a line with the normal fillet almost to the terminal point. Then heat the mitred fillet and run it in the line. As you approach the end of the line, keep the fillet in place and turn the wheel with your hand so that mitre hits at the planned endpoint.
  2. A matching pallet
    If you have a pallet of the same line thickness as your fillet, you can stop the wheel short of the terminal point of the line. Simply use the pallet to make the remaining line.
  3. Overstamping
    For this procedure, you simply stop the wheel when the line tapers off where you want the it to end. Then take a ornament and stamp it over the end of the line. This technique is also used to cover the joins between two lines at the corner of a frame.