The other thing to note is to be careful of diecast cars in 1/18 as they seem to vary in how they did the scaling (looks like more to fit the box than actual scaling), motorbikes work well but you find that you may be unable to fit your 3 3/4 or 1/18 figures into a 1/18 car.

BTW the 25th anniversary line, while classed as 3 3/4 seems closer to four inch to me