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This is a set of two thumbs, one that is farily curved with solid area between points, and the second which is straighter and open between the points, which are serrated for firmer gripping of material. There are extra pins included, but I'd suggest replacing pins with metal such as brass or piano wire. I did make a pin on the bottom of the mount where it attaches to the excavator arm, but that is not a requirement. However, drilling a hole and using that as a help to glue the mount to the arm would certainly make it stronger. This piece is designed to fit the Diecast masters caterpillar hydraulic excavator. Should there be a question or concern, contact me via the designer link or via email to firstname.lastname@example.org