Abstract: An improved molding apparatus which includes a lower mold part containing a seat to permit a wheel to be locked thereon to form a mold cavity between the upper surface of the lower mold part and under surface of the wheel, said wheel having openings therein including at least openings for mounting the wheel on an axle and for charging the cavity with molding material, a sealing means for sealing the openings in the wheel, said sealing means being pivotable about the lower mold part by a pivot frame to bring the sealing means into a locked sealing relationship through an elastomeric gasket, said gasket in the locked sealing relationship being under uniform compression, said uniform compression being achieved by action of at least three springs located around the seal means and between the pivot frame.