If you mean the handle, the taper is a device to let the handle part of the lid pattern retract before the pattern is removed from the mold. Wagner handles are also like this, just not as tapered. Earlier techniques used hinged, retractable halves, so those handles are really two prongs which meet tightly together. If not as tightly as intended, the small separation is sometimes misidentified as a crack.Doug, it it a hallmark of BSR lids that they are thicker around on one end than the other? And are any other brands like that? Thanks.
See also: http://www.castironcollector.com/casting.php