Internal through hole opened up to a maximum of 9/16″. Please note that while this allows larger stock to pass through the headstock, it also eliminates the #1 Morse internal taper, meaning tapered tools like drill chucks, fly cutters, etc. cannot be held in the headstock. It is also not compatible with the thread cutting attachment or lever collet closer.
Threaded tools can still be used such as 3/4 jaw chucks and end mill holders.