Some are small, round holes just large enough to accommodate a penis and nothing more. In some bookstores, they can be larger, rectangular or square cut-outs big enough for a person to place his or her head through if so inclined. Why so large? While the glory hole is large enough to allow two people to engage in oral sex or masturbation, one person at a time, the larger ones allow easier access not only for the same purpose, but can also allow for anal intercourse, or vaginal intercourse if you happen to be female, or on the outside chance you meet a woman there. Not that you have to do any of this. We have to believe that while the larger holes when used for oral sex gives one person better access to the instrument of destruction, and surrounding parts poking through, they would also add to the exhibitionist and/or voyeuristic nature of the experience for both parties.