There are 3 stub drill bit sizes:

The 5/16″ and 11/32″ stub drill bits have a 1 3/4″ flute length and the total length is 3 1/16″. The standard wood bit is longer and tends to “wander” if it hits a tight wood grain.

You may also like to buy the Bottoming Tap which cuts threads to the flat bottom.   This is recommended for the hard exotic wood.

The 7/16″ stub bit is used for the Threaded Inserts   Some wood or especially acrylic and resins do not hold threads well and the brass inserts make it a lot easier.

Lathes Specifications: here is a list of lathe spindle sizes and Morse taper if you are not sure.

These drill bits are made in America