Radical 134
Radical 134 or radical mortar meaning "mortar" or "joint" is one of the 29 Kangxi radicals composed of 6 strokes.
In the Kangxi Dictionary, there are 71 characters to be found under this radical.
臼 is also the 136th indexing component in the Table of Indexing Chinese Character Components predominantly adopted by Simplified Chinese dictionaries published in mainland China, with ? being its associated indexing component.