8-piece steel Dowel Tenon Center Set contains two each 1/4, 5/16, 3/8, and 1/2 inch dowel centers.. Dowel centers allow you to precisely transfer the location of dowel holes in one board to the same location in another board. Because of the counter-bored back you can also slip them over a dowel to precisely mark locations. To use, simply insert a dowel center into a hole, then line up the second board to be joined and press the two boards together. The exact center location is now transferred into the second board ready to be drilled. Indispensable for doweling to join boards.