This feels a bit like consulting the Oracle at Delphi. I have faith but are you lot really all-knowing? 
I was making a plasma cutter. I had lots of sneaky ideas to try out that was going to make it the bestest plasma cutter in the world. But then I fitted my first T5 belt on a T5 pulley and everything came to a grinding halt.

There is about a millimeter of slop on it 
All making stopped. The only good belting available that fitted the bill was steel reinforced T5x16 and it didn't cut the mustard. Everybody else using it doesn't care about plus minus a millimeter or is there a secret pulley supplier you are all privy to but I don't know about?
What gives? 