How to Select the Proper Spark Arester...
 

If the diameter of the spark arrester inlet is as large as the exhaust pipe, restriction generally will be within engine guidelines.  However, to be sure, you should check the exhaust CFM of the engine against the CFM rating of the spark arrester.  Some applications (e.g. turbo-charged and two-cycle diesel engines) may require larger arresters and an adapter will be needed to complete the installation.

Nelson Standard Spark Arresters....
Nelson Spark Arresters are designed for universal application with a minimum of restriction on the engine. They work well as add-on units to existing exhaust systems. Their light weight and small size reduce stress and vibration to the rest of the exhaust system.  Typicall applications include logging and construction equipment, agricultural machinery, over-the-road trucks, airpor equipment, forestry and military vehicles.