Ya the 5mm does the muffler bolts on most that don't have 4mm. Buy a dental pick and clean out the heads, they're 5mm Silly Stihl guy thinks Huskys will be just as complicated and difficult to work on :banana:
Many of the 200 series (268, 266, 288, etc.) need a 3/16 (not 4.5mm) hex wrench to remove the head bolts. Everything else is 4 or 5mm.
Dental pick? Look at Mr. Fancy Pants over here. I just use the next size down wrench and spin it in the hex cup.