L-15200,L-15210andL-15220are very similar. L-15200 has a smaller center dot. The last three pictures are another example of the knob. See L-15220 for side views of all three knobs. Corbin, Lockwood & Sargent (1901 p. 56) made 20 fluted knobs. Pictured below is a window in the design for Corbin 1895 fluted knob. The pair shows the 2 1/2 inch and 2 1/4 knobs.