can anyone tell my why weber uses fiber washers on the wsm ?? don't make sense.

I'd guess it is to reduce the chance that the bolt head would crack the porcelain when you're assembling the WSM and tightening down the nuts. The surface of the center section is curved, the bolt head is flat. Without some kind of resilient washer you stand a good chance of dimpling the metal and cracking the porcelain. I think it makes perfect sense.

i can kinda see that though the washer is a hard fiber washer so doubt it prevents bending. maybe just to prevent scratches.

Yea, it's kinda weird that they only use them on the outside at the grate strap bolts. But the legs are just bolted metal to metal. That doesn't make sense to me. You'd think there would be a fiber washer added there also.

Tim