String Trimmers

I have a 128 Djx and I tried the blade. When starting up with the blade, there was a lot of vibration which caused the screw holding my shield to fall off when I started cutting the tall grass. Needless to say, I lost the screw in the tall grass. Is the vibration natural for a blade? I do not have a wrench which tells me how many pounds of pressure I am using to attach the blade. Do I have to tighten the blade very very tight? After the initial start up, the vibration goes away. I have not used the blade since then.