These tools are designed to split stone when driven into a drilled hole or a natural crack in the stone. Also know as Wedge and Shims or Wedges and Feathers, they are among the oldest styled tools still used today and remain one of the best methods of splitting stone.
They come in sizes from 5/8” up to 1½”. Length increases with width. The smaller sized are used by stone masons to split rocks down to workable dimensions. The larger sizes are used for splitting sections of stone during quarrying or for splitting large rocks.
To use this tool, you place the feathers into the hole so that the flat sides of the plug will be parallel to the line where you wish to split to happen. The plug is driven into the slot between the feathers until the stone splits. If it becomes stuck, the plug is tapped back and forth until it comes loose, and then you begin again. Driving the plug between the feathers forces them against the sides of the hole and splits the rock.
Different size plug and feathers are used in different size holes. To be work correctly, the diameter of the plug rod and feathers, at the point where the rod meets the feathers, must be larger than the diameter of the hole. Additionally, the drilled holes must be straight to keep the tool from binding.
Source: Granite City Tool Company, St. Cloud, Minnesota