The alignment bar references the center of the frog. Suggested Use First the hoof is trimmed and prepared for the shoeing. The horseshoe is then shaped to fit the hoof and ready to nail. At this point a farrier could use an extra hand. When nailing the shoe the nails are driven into the hoof at a 50 to 60 degree angle causing the shoe to slide back from the intended starting place.
Shoes can twist while nailing and end up installed crooked.
The two locator pins hold it in place against the horse's hoof wall of to each side of the center. Now you are ready to nail the shoe on. Place it into your toolbox and finish driving the nails in place. If the shoe moves, put it back in place and drive the other nails and clinch. Repeat on the remaining shoes.