Strap on dildos and harnesses are a popular addition to many lesbians and straight couples bedrooms. Much like regular dildos, strap ons come in many different shapes and sizes. Hollow strap ons, or penis extenders as they are often referred, are a good option for a man who would like to penetrate his partner with a bigger penis than his own or for men with erectile problems. Double dong sets allow for both partners to be penetrated at the same time.