The idiom of "'Bo' and 'Zhong', Almost The Same--Bo Zhong Zhi Jian" is from "Dian Lun (典论)", the earliest literary critique in Chinese literature history, whose another is Emperor Wen of the state of Wei in Three King Kingdoms period of China.
In it, while talking about the literary talents and achievements of Fu Yi (傅毅) and Ban Gu (班固), two contemporary litterateurs of Eastern Han Dynasty, Emperor Wen said that the two were like 'Bo' and 'Zhong', almost the same.
In China, traditionally, 'Bo (伯)' and 'Zhong (仲)' along with 'Shun (叔)' and 'Ji (季)' are the most common four characters to name boys of a family, since the four characters stand for the order of age. This tradition dates from 3500 years ago Zhou Dynasty of China.
'Bo (伯)', or sometimes 'Meng (孟)'： the oldest son; 'Zhong (仲)': the second son;
'Shun (叔)': the third son;
'Ji (季)': the fourth son.
Therefore, what Emperor Wen said was Fu Yi and Ban Gu'Bo' were like brothers, almost the same.
Besides, in China, a polite way to call brothers of a family is to address them "Kun Zhong (昆仲)". For example, there are two brothers whose surname is Li, so you can call them "Li Jia Kun Zhong (李家昆仲， the brothers of Li's)".
Background and Writer Comment:Ban Gu and Fu Yi were both the masters of Fu, a literary form, sentimental or descriptive prose, often rhymed, popular in the western and eastern Han Dynasty and Three King Kingdoms period. In addition, Ban Gu was also an outstanding Chinese historian best known for his part in compiling the Book of Han.
The idiom of 'Bo' and 'Zhong', Almost The Same--Bo Zhong Zhi Jian refers to being almost the same, very similar with the English phrase: "nip and tuck"