Steel and aluminum don't like each other! that's why you are getting the binding. Only use Stainless steel with aluminum. And of course never use aluminum fasteners for an application like this due to strength. And use all nylon washer if you can or between the SS washer and where is touches the moving part.
The ISO metric bolt has its diameter as the numeral part of the name.
So M8 has a diameter of 8mm compared to that of the M4 bolt. So far scaling would make sense.
However, the pitch of them is not proportional and would be wrong if you scale them.
her is a figure from Wikipedia. Wiki