[填空题]
To make a secure fit, rivets that are larger than the ribma-9336cfxaq(cvud ;e j 3ybvet holzjods:+(sop (f xhb-6e are often used and the rivet is cooled (usually in dry ice) before it is placed in the hole. A steebdszos(-:jh+( fox 6 pl rivet 1.871 cm in diameter is to be placed in a hole 1.869 cm in diameter at 20 $^{\circ} $ C. To what temperature must the rivet be cooled if it is to fit in the hole? $^{\circ} $ C