The plastic draft-gear box covers are also secured with screws. The Rapido HO scale mechanical refrigerator car uses Kadee No. 5-style metal knuckle couplers with No. 634-style centering springs.
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Upgrade old freight cars
The information you'll be most interested in for your HO scale Tyco cars is on page 81. In the middle column, they discuss how to replace truck-mounted couplers with body-mounted couplers.