I needed a tidy counterweight for my Drawbot. I tried designing some different cantilevered pen holders with little success but did learn some stuff along the way. First the basic pen holder works good with about 3 oz of weight hanging off it it for a sharpie. Second, as well as the ball bearings work- i'd rather use them for something else.

I threw this together with the intention of filling it with sand - but like half the the stuff on the internet the weight per cc was off but 2x on the site I found it on. Fortunately for me the design I came up with is also the perfect size for a stack of nickels.

1) Print:
2) Fill with nickels (but not up to the very top)
3) Screw M5-10 screw through the hole in the lid and thread a nut onto the back.
4) Generously apply acetone and glue the lid on.

I looked on Amazon for 3 Oz fishing weights but they wanted $7.95 for 5 of them - this is far cheaper.

Once the glue has set I used a little piece of monofilament to hang it off the pen holder. The monofilament should loop around the screw and hang over the front. I'm able to print on a completely vertical surface with this now.