How are si units used in the united states?

SI (metric) units are used in the United States to manufacture anything
that you want to be able to sell outside the country, and to buy anything
that comes from outside the country.

It's only when the material or object starts out in the US and stays here
permanently that SI units are NOT used.  This is because the metric
system is too hard for people in the US to figure out, understand, or learn. 
Whenever anybody hears any rumor that it would be a good idea for the
US to join the rest of the world and change to the metric system, our
citizens scream bitter tears to their elected representatives in Congress,
reminding them that the metric system is too hard for us, and that we will
vote them out of office if they force it on us.  We will be hopelessly lost
and confused if we are not allowed to keep the system that we know and
understand, along with both of the other countries in the world (Burma and
Liberia) where the same system is still used.