The overhang is the amount of leather projecting beyond the left/right hand edges of the paper inside - with four average sized journal refills loaded (approx 34 leaves each). The more you pack in, the larger the overhang you’ll want.

If you do not leave me a note telling me the width you need, I will make it STANDARD, as default.

The width measurements are shown here:

STANDARD: Approx 10mm

ULTRA: Approx 17mm (If you really want to fill that journal jam pack full, or are using slightly thicker journals.)

EXTREME: Approx 23mm (OK, this is over the top, but some folks want to do wild things with their journals :-) )

I hear you ask, wouldn't just changing the size of the spine make the same difference?

The answer is yes, it would, but as changing the spine width equates to changing the overall width, I find this method is simpler to relate to.