Peixi 佩觿 "The spike of the girdle" is a book on Chinese characters written by the Song-period scholar Guo Zhongshu 郭忠恕 (d. 977), who also compiled the book Hanjian 汗簡.
The title of his 3-juan long book Peixi is derived from a verse in the Shijing 詩經 "Book of Songs", which says that "There is that lad, with the spike at his girdle" (transl. Legge 1871). Guo wanted to express that his book was indispensable for the studied of ancient texts, like the spike of a girdle.
The first part of the book describes how and why characters changed over time, namely by shape and sound, and which errors usually occurred when copying a text. The second and third part of the book concretely compare characters that can easily confused by either shape or by sound. They are arranged phonetically. There is an appendix with errata that was added by a later person.
The Peixi is included in the series Siku quanshu 四庫全書, Tiehuaguan congshu 鐵華館叢書, Congshu jicheng chubian 叢書集成初編, Tang-Song congshu 唐宋叢書, Xu Zhibuzuzhai congshu 續知不足齋叢書 and Qingfentang congshu 清芬堂叢書.
Li Xueqin 李學勤, Lü Wenyu 呂文鬰 (1996). Siku da cidian 四庫大辭典, Changchun: Jilin daxue chubanshe, vol. 1, p. 732.
Mei Yue 梅悦 (2015). "Peixi yanjiu zongshu 《佩觿》研究綜述", Wenjiao ziliao 文教資料, 2015 (4).
Pan Yinsheng 潘寅生, Guo Jiankui 郭建魁, ed. (1993). Zhonghua shehui kexue gongjushu cidian 中華社會科學工具書辭典 (Lanzhou: Gansu renmin chubanshe), 365.
Wu Feng 吳楓, ed. (1987). Jianming Zhongguo guji cidian 簡明中國古籍辭典 (Changchun: Jilin wenshi chubanshe), 523.