The Park Tool DT-3 Bicycle Disc Rotor Truing Gauge is a disc brake tool designed to help cyclists maintain their bike's braking system. Made in the United States, this tool is specifically designed for truing disc brake rotors. The DT-3 model is a reliable and accurate tool that ensures the proper alignment of the rotor, which is essential for optimal braking performance. I purchased this gauge about 5 years ago. I opened the box and closed the box (haha). It's never been assembled, so it's never been used! It's just been sitting in the garage this whole time. I'm selling this as I still don't see myself using this. I hope someone can put it to good use!