These small "squeegees" are made of brass with felt-covered blades; they allow you to quickly reach through the strings of a grand piano to dust the soundboard. Use your vacuum to pull the dust off the cleaner each time it is withdrawn from the strings. For very dirty boards, use the cleaner to push a dampened cloth; this allows more pressure to be applied and gives more even coverage than is possible with a conventional soundboard steel, and they won't scratch the soundboard.
A set includes three sizes to work in different areas of the soundboard:
Large - 3 3/4" blade with 22" handle for reaching under the bass strings and reaching through plate holes to the back side of the bridge.