By the end of that year, all Steinway & Sons pianos manufactured in the United States use Permafree (Teflon) bushings. Steinway & Sons advertisement begin to mention maintenance-free pianos for any climate. (In reality, it’s precisely Teflon’s lack of response to changes in humidity that will lead to major maintenance problems: even though Teflon doesn’t expand or shrink, depending on changes in climate, the wood that surrounds it does. During the humid months of summer the wood expands, and the Teflon bushings get loose in their holes and begin to make knocking noises; in dry winter the wood shrinks and squeezes the bushing so tight that the keys begin to get stuck. This problem will lead to a sudden avalanche of complaints three years later (see the corresponding 1965 entries).