Took me two attempts but I have now developed an OpenSCAD model to produce accurate horizontal holes. I.e. a shape that, when sliced by sampling it the middle of each layer causes all the rounded filament edges to touch the circle tangentially. Handy when you want a snug fit but there is no access for a reamer. Also if you do use it to make an undersized hole to ream it should more accurately guide the reamer. If you just subtract a cylinder and print it you don't get a round hole.