A drill tap, or drill and tap bit, is a tool head that combines a traditional drill bit with the ability to add threads to the hole as it is drilled. A drill and tap bit allows a bolt to fasten into a metallic object.
Traditional taps for adding threads require a predrilled hole. The drill tap allows these two steps to be combined, saving time.
As there are many variations of thread counts for each diameter hole, a drill tap is less flexible than separate drill bit and tap sets. Therefore, it is more costly to purchase drill taps that cover all possible combinations.