In principle, men can use any size they can accommodate, and larger models are more efficient. However, as with vaginal use, it is impossible to determine the appropriate size based on biometric data such as age, height, build, etc. It should also be possible for any man without anal experience to take a 36 mm size after a short preparation, provided there is no disease in the anal area or psychological causes. In rare cases, the elasticity of the anal muscle is the cause of problems; human stools often have a larger diameter. But inside the body - that is, according to the female principle - the (unconscious) ego usually wants to prevent an opening, wants to hold on to the traditional male image, to religious conditioning, etc. Many men find it very difficult to overcome the hurdle of overcoming deep-seated patterns. But "allowing instead of letting go" is an extraordinarily enriching experience of the female principle, of taking in, literally: of integrating. All people have both female and male parts, one cannot function without the other according to the fundamental law of polarity. When both principles are activated, potency problems often resolve unexpectedly - the "stream" of life flows again. And experiencing the other side within oneself broadens the horizon for many other fundamental connections in life. This physical manifestation of "opening up" or surrendering to the opening of the body through one's partner will also open up the psyche. This ancient hermetic principle "Below as above - above as below" is also used in yoga, Tai Chi and similar techniques. With the Theros FMS dilators you can venture into new territory in a self-experiment if the initial size of 36 mm should be problematic - also for intensive and proven healthy prostate massage. Or a woman could use dilators to gently "expand" the shared horizon of experience with her partner and at the same time explore the male principle within herself that is equally necessary for a holistic experience - an exciting and connecting enrichment of the shared erotic experience. But be patient with yourself or with your partner, the journey is the destination. Then "allowing instead of letting go" will be an equally wonderful experience for both partners.