Angelo, Thanks very much :-)
Greg, Thanks! Yes, it is the GPS blank. And yes, the flange is attached by gluing it into a slot cut into the resin. Many penmakers also put a small pin in through the back of the penholder to hold it in place, but I don't do that (I figure that if the glue fails it's much easier to glue it back into place than if it has a pin also holding it). I actually used to make them so that they were removable, with no glue involved - a thin piece of wooden dowel is inserted into a hole drilled down through the end of the pen holds the flange in place - but that also has issues and doesn't look as nice.