That of course was the Mars Climate Orbiter and other problems kept people from discovering the error. So were other federal agencies. I can walk down to Lowe's or Home Depot and get metric nuts and bolts. Your American-made cars have been metric for years. For NASA to purchase hardware in the USA, they MUST specify English units.
Shop tries to makes part.
Shop orders metric tooling. Shop finally makes part. They also find it easier to work in metric units than in the old ones. And the shops that aren't doing metric had better start or their business is going to decline. Multiply that by the thousands of parts that go into one spacecraft or Space Station component.