I know I can use the Width Mate in Advanced Mate option to add a mate between the flat side of a slot and a hole but how do I center the hole in the slot between the two Arcs of the slot? What is the best mate option to use rather than add a distance mate or adding extra features like planes etc?
If your slots were created using the Slot tool on the Sketch toolbar, then when you turn on temporary axes there should be one at the center of the slot. You can use a concentric mate between this temporary axis and your hole. Then you won't need the Width Mate.