Why do you want to run wheel spacers to begin with? What is your end goal here?
Are you running wheels that are a different offset/width than the factory wheels and are wanting to correct the fitment, or are you running the factory wheels and just want a wider stance?
I have 19mm (3/4") spacers installed on mine, this was to correct the fitment from the higher +ve offset wheels I purchased as well as to get a slightly wider stance to compensate a bit for the larger tires and eventual lift kit.
Whichever spacer you decide on, make sure it is a hubcentric one so the wheel can be mounted correctly and the weight is carried by the wheel hub and not the lugnut studs.
Spacers beyond 12mm thick will usually come with their own set of pressed in studs that the wheel mounts to, with the spacer bolting onto the factory studs, spacers less than 1" thick will require you to cut your factory studs because they will stick out too far beyond the mounting face on the spacer blocking the wheel from being installed correctly.
2020 Canadian LE in Quartz Brown
225/75r16 Cooper Discoverer AT3 4S tires on 2017 Mitsubishi Lancer Wheels
40mm suspension lift *soon*