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https://a.co/d/0cJP6Fxe Holes, round/slotted are drilled/cut in top of the stringer. Then a steel rods turned to a sharp point like a pencil is inserted into the hole with the point barely above the surface. Then the tread plank is played on the surface of the stringer and when in position it is struck to transfer the location of the stringer hole to the underside of the tread. The points are removed and dowels/dominoes are inserted into the hole with glue. They are projecting a significant fraction of the thickness of the tread above the surface of the stringer. The projecting end of the dowel/dominoes has a saw cut halfway through it to accept a small wooden wedge properly sized. It is smeared with glue also. When the tread plank is set down over the dowel/dominoe it is knocked hammered down with a mallet. The wedge driven by the tread expands within the hole in the tread helping to lock the tread in place until the glue cures.
Do you know what dominoes are in this context? https://a.co/d/0cJP6Fxe