This custom drill bit can be used with our patented Dor-Cor Drilling Tool (door core drill fixture), or used separately if you need a long drill bit to drill the width of a door. We don't recommend that you use this on fire rated doors. You can use it on listed doors, so long as you are a certified person under the Perfect Raceway Program. The PRP is managed by Intertek Testing Services, under the Warnock Hersey name brand. If you need a replacement bit for your Dor-Cor, or you are just looking for a very well made custom door drilling bit, this is the one you want to order.