You can get those inserts at Home Depot for cheap. I replaced the tee nuts on my model 19s and I've used them on a couple of other 416 applications. They work great and they don't pop out like tee nuts are apt to. The slots on a 416 or 604 and the like have enough clearance with a 3/16" bolt for home quality hole location. I have no idea why people always seem to suggest tee nuts for speaker cabs.