Copied from a period shutter knob shaft that can be assembled to any suitable knob.  The price includes the assembly to the knob of your choice.  Order the knob/knobs separately and give your instruction in the comments section of the order form.

Length (not inc fixing stub): 2″ (51mm)

Square Section: 5/16″ (8mm)

Tapering to: 1/4″ (7mm)