Ernest2,the question you want to be asking first is what brand of carb is commonly used on Stihl engines?The engine shop should be able to tell you that as they are the ones selling them.Once you have narrowed down what brand of carbs they are able to order,then you can narrow down the search for a 11.1mm size venturi carb.I am sure though that there is someone here in this forum that knows the answer to that question already regarding Stihl products and the carb brands that they use.Any Zama or Walbro brand carb with a venturi size of 11.1mm should suffice.Be aware that a brand new carburetor from your local small engine shop can get to be quite pricey.Look to see if any any used carbs are available first and you might be able to save a few bucks.