124X12 is a size of Dremel bit, commonly used for drilling, engraving, routing, and milling materials like wood, plastic, and metal. It is a cylinder-shaped cutting bit that has a diameter of 1/2 inch and a length of 12 millimeters. This size of bit is great for cutting intricate, detailed shapes with precision, as well as drilling and milling. This bit can be used with a variety of materials, including wood and plastic, to create detailed designs.