Thanks Brian. The pen is called a Moore Banker, from what I can tell this is the largest size they made it in a #6 size. Interestingly enough it is not a thumb filler, you place your thumb in the slot while screwing on and off the cap to help protect the nib from otherwise potentially being damaged.
I suppose it's about time I post my pens of 2015, I promised Brian I would today!
There was a theme for 2015, Grieshabers & Hard Rubber. I collect larger Grieshaber pens, and the vast majority of my collection consists of pens from the 1920's through 1940's. I was able to add a few examples this year, all with large #8 Grieshaber or Sager nibs. I also added a couple of gorgeous Moore Safety pens and a Snapfil pen marked General Manufacturing. Not a huge group from 2015 but some pens that just don't come up too often.