These filigree pen blanks are intended for advanced pen makers and are designed for the 8mm metallo pen kit available from Penn State Industries in chrome or gold finishes. The "sleeve" series of blanks have outside diameters that are slightly less than the correct final size for this pen kit (396 mils OD vs 426 mils OD). The sleeves are intended to be cast molded into place on the pen kit brass tubes using a clear or translucent resin through which the sleeve filigree patterns are visible.
The radial thickness of the sleeve wall is determined by minimum design rule dimensions of the 3D printing process. To reduce the height of the sleeve material it may first be glued to the brass tube and then carefully sanded or turned to a thinner dimension on a lathe before being cast molded into the resin. The underlying brass tube may also first be painted to provide a contrasting color for the sleeve. After molding the blank with resin use standard pen making techniques to trim the ends of the tube flat, and then turn and polish your blank on a lathe prior to final pen assembly
For final pen assembly it helps to use a dedicated pen press to achieve good results. Alternately you could use a large C-clamp with wood or plastic covering the clamping faces but you need to be extremely careful to not crush or damage your pen mechanism.