This is one of a series of crochet vehicles I made for my children. The back of the trailer is hollow and can be attached so that the door opens at the top or at the bottom depending on if you would like it to be one that carries a small race car (you can fit two of my mini race cars in the truck perfectly) or if you want it to be a truck that takes other cargo. The trailer is attached to the cab of the truck using a button on the back of the cab and a buttonhole on the front of the trailer.
Cab: Length 10.5 cm (4.1”), height 10.5 cm (4.1”), width 10 cm (3.9”)
Trailer: Length 22 cm (8.7“), height 10.5 cm (4.5“), width 10 cm (3.9“)

While most of my patterns can be made using a different weight yarn and hook. I would not recommend anything lighter weight than DK weight. If you use a heavier weight yarn then you may need to use bigger buttons for closing the back of the truck and for joining the truck and trailer unit together.