Radical 66 or radical tap (攴部) meaning "tap" is one of the 34 Kangxi radicals (214 radicals in total) composed of 4 strokes. It is also used to represent a folding chair.
In the Kangxi Dictionary, there are 296 characters (out of 49,030) to be found under this radical.
Fazzioli, Edoardo (1987). Chinese calligraphy : from pictograph to ideogram : the history of 214 essential Chinese/Japanese characters. calligraphy by Rebecca Hon Ko. New York: Abbeville Press. ISBN0-89659-774-1.
GF 0011-2009 Table of Indexing Chinese Character Components prescribes 201 principle indexing components and 100 associated indexing components (in brackets) used in Simplified Chinese. Not all associated indexing components are listed above.