3026 is similar to #3027. It is taller Apx >300 (7.5mm) tall the 6 recessed areas for inlay are 3/16 sq and the dia. is apx.500 (13mm) It is relief cut to fit over the bottom barrel
Not as tall as #3026 it is .250 (4mm) tall the 6 recessed areas for inlay are aprox 1/8x 3/16wide It is aprox .500(13mm) in diameter relief cut on the bottom to fit over the lower barrel.
This is the center piece for the custom Sierra style pens. the lower tube fits into an 8mm tube and the top fits the standard 10.5mm upper tubes. You can tap the upper with an 8.4x1mm tap or solder an 8mm tube in and trim it to fit an 8mm transmission coupler.