I've gone down a Torben Holmbäck rabbit hole.  This is part of a four piece desk set of "blocks" designed by Holmbäck.   All of the blocks have the same external dimensions (70 x 105 x 42 mm).   All were originally machined from a block of black anodized aluminum.  This is one of two different pen/pencil holder blocks in the set.  

I've added a cavity in the base that allows you to add self-adhesive wheel weights to give it some heft.  The cavity is designed to hold these wheel weights (Amazon:  https://a.co/d/1S71y2b) in a 3 high stack of 2x2 weights for Pencil Block 1.  I haven't printed these yet but will post pictures when complete.