Hey ~ I don't MAKE them :) Nor do I WRITE the Manufacturers Description :) Apparently my 'Google" Research says ~ They got a smooth surface with MODERN molding techniques :)
Actually my "Google' research says ~ Recent achievements, specifically in iron sand metal casting, has lead to thin-walled iron components that can maintain structural integrity and compete with lightweight (aluminum, magnesium, etc.) castings without unnecessarily raising the weight of the component.
What will these MODERN advancements come up with next?
Again though ~ I don't MAKE them :) Nor do I WRITE the Manufacturers Description :)