I have a husqvarna 250rj trimmer that includes a trimmer blade for small brush. I cannot figure out how to assemble based on the manual. I seem to have all the parts but when assembled per the manual, the blade does not seem to have anything "holding" it on the drive shaft. The blade support bolts on to the end but the blade "free wheels" on the shaft Am I missing a piece that the manual does not show clearly???