3.  In bolted installations, use spacers, collars, shoulders,  or stop-nuts to prevent tightening the bolt excessively.  Whenever such devices are used by the aircraft  manufacturer, retain them in the replacement  installation. It is important that the original number  of bolts, complete with washers, spacers, etc., be  used. When rivets are used, provide adequate spacers  or other satisfactory means to prevent excessive  tightening of the frame to the plastic. 4.  Mount plastic panels between rubber, cork, or other  gasket material to make the installation waterproof, to  reduce vibration, and to help to distribute compressive  stresses on the plastic. 5.  Plastics expand and contract considerably more than  the metal channels in which they are mounted. Mount  windshield panels to a sufficient depth in the channel  to prevent it from falling out when the panel contracts  at low temperatures or deforms under load. When  the manufacturer’s original design permits, mount  panels to a minimum depth of 1 1 ⁄ 8 -inches, and with a  clearance of  1 ⁄ 8 -inch between the plastic and bottom  of the channel. 6.  In installations involving bolts or rivets, make the  holes through the plastic oversize by  1 ⁄ 8 -inch and  center so that the plastic does not bind or crack at  the edge of the holes. The use of slotted holes is also  recommended. 7-58