characterized by a central array of coring holes 46 separated from one another by webs 48 the coring holes 46 in the central array are substantially opposite the top surface 28 and terminate short of the top surface 28 by a distance approximately equal to the thickness of the webs 48 and the webs 44 similarly arrays of side coring holes 52 and 54 extend into portions of the bottom surface 18 aligned respectively with the side surfaces 34 and 36 of the body 12 the side coring holes 52 and 54 are separated from one another by webs 56 and 58 the coring holes 52 and 54 terminate short of the side surfaces 34 and 36 by distances approximately equal to the thickness of the webs 48 56 and 58 additionally the coring holes 54 and 56 are spaced from the depressions 38 and 40 by substantially the thickness of the webs 48 56 and 58 hence the body 12 has substantially uniformly thick walls throughout and can be molded efficiently without sink marks short shots or the like the bottom surface 18 as shown in fig3 is divided into four quadrants a b c and d the quadrants meet at a location midway between the front and rear edges 20 and 22 and midway between the first and second side edges 24 and 26 each quadrant a b c and d is characterized by an array of substantially parallel grooves 60 that extend out from the intersection of the respective quadrant with adjacent quadrants the grooves 60 then.