Some aftermarket exhausts have thicker flanges than the stock exhaust, particularly those that are made of aluminum to help prevent warping.  These longer bolts will replace the stock length bolts that are too short in those applications. Sold in sets of 6.
 
"Not to be used on stock exhausts or aftermarket exhausts with flanges the same as the stock thickness"
 
It is highly recommended to use high-temp anti-seize on exhaust bolts.