I'm borrowing my dad's Milwaukee 4 1/2" electric grinder for this weekened's projects and I bought some 4 1/2 x .040" x 7/8 cutting discs. They fit it perfectly, but they're too thin so they won't tighten up. Is this an indication that I shouldn't use these thin cutting discs in this grinder, or should I just use a washer to make up the difference and go for it? The plate that holds the discs says to turn it over for 1/8" thick discs, but even when it's flipped over, it won't tighten against these thin cuttind discs. Do I have to get an 1/8" cutting disc or is it safe to cheat and make these work?