Size/grade of HO ballast?

[RobertInOntario]

If you look at prototype ballast, I think most of the rock is probably about 3-5 inches in diameter. I ho scale, 3.5mm=1 foot. 3.5mm is just slightly bigger than 1/8 inch. If the ballast you are looking at has pieces 1/8 of an inch in diameter, that would be the equivalent of rocks 12 inches in diameter. If the rock is bigger than 1/16 inch in diameter in any direction it is oversize for ho.

Thanks for these comparisons, Russ. I think my coarse ballast is only about 1.5 mm in diameter so I think I should be OK. I'll check it more carefully later. Rob