I don’t know for certain, but I’d think it would be the series number and model number. Collectors use info like that either to make sure they’ve collected all the items in a series, or just to better identify the models.

Hot Wheels Collector numbers don’t seem to follow the pattern of number/number, they are sequential numbers, but the series numbers are depicted as number/number, see link

I have seen those too. Some examples are 3/10. That is too low a number to be a series number, as Hot Wheels have been around forever and to only be on the 10th series or the 3rd series is too unbelievable. Also, I think multiple models have the same numbers so it could not be the car number or model.

@jca Each new series that comes out is numbered, much like an artist numbers their canvases. So if this new series will have 50 cars in it, they will be number 01/50, 02/50 etc. See link above.

What I think it is is that 1 would mean the first one made and there only how many made of what the second number says.