Some gaps are kinda cute. Others are just plain scary. The gap on a bench grinder? You may not give it much thought. But if it’s there’s too much space between the wheel and the work rest, the odds are good that something- a piece of metal, maybe your thumb- is gonna get sucked in. *metal clang Set the gap to no more than an eighth of an inch. You’ll need to readjust it occasionally as the wheel wears down. The upper guard is there to knock down any flying debris. It should be set at no more than a quarter inch. If you’re using a wire brush, there’s even more risk of being pulled in. It might be better to remove the work rest entirely. Remember, nothing’s a hundred percent. ALWAYS wear hearing and eye protection. It’s your best bet for staying safe.