ok i need help i broke the blade to my mower and i got a universal blade i can't get it to stay tight because there is some kind of small blot im guessing or something that keeps the blade from moving. well theres only one little blot thing there it looks like one has come off of the thing you would attach the blade too. and i think thats why my blade won't stay tight on my mower can you help me out? plz. thank you