The center band is made from laminated Cocobolo turned into a round rod, drilled with a 6.8mm drill bit, cut to length, then glued onto either the top of bottom blank.
The other blank is cut back to expose the brass tube.
This bit of exposed brass tube fits into the 6.8mm center band hole and helps with alignment.
The black grooves are blackened with a sharpie before final sanding and finishing.
This pen was made from laminated pink ivory wood and needed no finish ... just polishing.