any portion of the mold having wear or a gap that can cause the formation of flash as is evident in fig2 the shim 20 is formed of two circular sheets 22 and 23 of elastomer material that are fused or joined together at their peripheries and form the said hollow interior 21 in those portions where the sheets are not so joined the darkened pattern shown on the sheet 23 represent areas where the two sheets of uncured elastomer are joined during curing leaving the other areas unconnected to form the hollow interior the hollow interior includes at least one annular passage 24 that extends entirely around the shim adjacent the location where the sheets are joined along their peripheries this allows for distribution or flow of liquid positioned within the hollow portion of the shim to any part of said hollow portion the hollow interior includes another concentric annular passage 25 closer to the center of the shim it being noted that these two concentric annular passages 24 and 25 are joined by a plurality of radially extending bridge passages 26 to assist in the distribution or flow of liquid throughout the hollow pattern fig3 and 5 illustrate the manner in which the hollow interior of the completed shim 20 is supplied with the liquid which may be any inert substance such as peanut oil the liquid is contained in the barrel of a hypodermic needle 27 and the needle is inserted between the sheets at the periphery of the shim and is moved far enough inwardly so that the tip of the needle resides in the annular passage 24 after a preselected amount of liquid has been introduced the needle is completely withdrawn and.