There is no maximum diameter, it just depends on how much you stretch it or insert an object to stretch it. I would say most people cannot take more than 3 inch diameter as that is a lot of stretch.
The anal canal has a ring of muscle, called the anal sphincter
The terminal portion of the large intestine forms the anal canal, which is the last part of the digestive tract before the anus. The anal canal begins at the anorectal junction and ends at the anal verge.
The anal canal serves to transmit and lubricate stool as it passes externally from the rectum
The anal canal
Anoscopy is the visual examination of the anal canal and lower rectum.Anoscopyits actually proctoscopy
Assholicus Maximus & Buttockical Minimus
anal canal
The function of the anal canal is to transmit and lubricate stool as it bypasses externally from the rectum.
The posterior portion of the perineum is called the anal triangle. It contains the anus and associated structures, such as the anal sphincters and anal canal.
Approximately half of anal cancers are squamous cell carcinomas, which arise from the cells lining the anal margin and the anal canal.
Rectum.
anal canal