Heavy duty 16 ga type 304 stainless steel aftermarket flavor bars for the Spirit ll E/S-310 grill. These are made with the proper taper on them and heat ports. The base measure 15.25" long and taper to 14.25" at the peak. These are the best you can buy for your late model Spirit ll three burner grill. If you have two burners you need a different set. 

Flavorizer Bars Replacement part for Weber Spirit ll 300 series grills.
 
Dimensions: 15.25” L x 2.687” W x 2.5” H. Package: Set of 5 flavor bars.
 

These are for the newest model of the Spirit 300 ll grills. They will not fit the older models that have the 22.5' long bars.  That set is part number 7537" search my other listings to see them.
Nor will they fit the last generation Spirit 300 grills. Those bars are part number #7636 and have no ports.

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Be sure to actually measure your old bars and check them against the size of this set. The length is all you need to know. This is the best way to avoid errors. Do not rely on the owner's manual, the internet, or your memory. Many customers think they own one model grill when they actually own another. If you are not certain please feel free to ask.  My return policy states that the buyer pays all return and replacement shipping charges should they order the wrong set.