Question: are all bowl pieces the same size?
Answer: For almost all bongs and dab rigs you only need to worry about two sizes: 14mm and 18mm. The image below shows you what your joint or bowl will look like compared to a dime. ... A 14mm male bowl piece is about 3/4 of the size of a dime whereas an 18mm male bowl piece is almost the entire size of a dime.