Snowballs stack to 16. If you shift click them into a BitHop, though, they stack to 64. I've tested this with a few modded items as well, such as Factory Tech's parts, which stack to 4. Any stackable item that doesn't stack to exactly 64 gets stacked to 64 when shift clicked into any BitHop inventory.

This doesn't happen when a hopper or another pipe inserts item into the BitHop, so it's safe for automation. It also doesn't stack unstackable items.