I bought these as a gift for my husband so he could try making Shaker style cabinet doors. We've used our router extensively, so we're very familiar with its features. He watched a few YouTube videos and then set the router to cut tongues. Beautifully cut! Then he installed the grooving bit and lined everything up perfectly. He let out a high-pitched screech as he turned on the router. Having never used these bits, I turned them off, checked everything for tightness and play, and turned them back on. The audio was insanely loud, not the usual router sound. So much so that I went to the garage because even I know what it's supposed to sound like. He headed the first board. It was a bit nerve wracking but we thought there might be a learning curve. The second stage went well, not perfect, but acceptable. Then rails. Then everything fell apart. It burned, cracked, cracked. Now it was the 3rd and 4th boards that ever touched that bar. Then a piece of wood and metal flew away and that was it. The ball bearing fell apart and ruined our parts. My husband was lucky that no shrapnel got stuck in his throat. I immediately contacted the seller who offered a full refund. I hope this experience helps another buyer. Maybe our beats were just a bad batch. We are buying another set from another seller so hopefully we can continue with our project.