Big, round coat hanger - 12cm in diameter, the same size as CD.
ABS bath smothing
Remember that ABS may shrink non uniformly, so you may need to scale internal thread in X and Y axis, but for Z axis keep 100% scale, otherwise thread won't match!
I printed hanger from ABS with 70% cubic infill and thick walls, and smoothed it IN acetone bath (not in vapour bath, it revealed infill on the outside) - 2 times for 3-5 seconds, and leaving it for 10 minutes to dry and harden after each time. Printing internal thread from different material helps a lot, because they wont melt into single piece during/after bath. Screw internal thread to piece of wood and screw hanger on it, it makes things lot easier to work with. I used PA12 nylon for internal thread.