Beta 1.0
The principal feature of any strap ons setup is the attachment the dildo is used to penetrate the other partner. While there is a huge array of different dildos available, most are attached to the harness in one of several ways. All methods have tradeoffs, and many couples will have different kinds of harnesses depending on which type of dildo they want to use.
The most common means of holding the dildo to the harness is to have an opening or ring in the harness through which a wide-based dildo is inserted. Cheaper harnesses tend to just have a round hole in the fabric or leather, while more expensive ones will use a steel or rubber ring. The advantage of this method is that dildos which fit are widely available and inexpensive, and even many dildos not meant for harness use will work in one of these harnesses, such as most dildos with testicles. The major disadvantage is the dildo is often held loosely (especially on cheap harnesses) and tends to flop downwards, and the dildo often can rotate in the harness, making it difficult or impossible to use g-spot or other shaped dildos.
Used primarily by Doc Johnson Vac-u-lock dildos have a rippled hollow in their base, which fits onto a matching plug on the harness or other toy. The advantage of this design is the dildo is firmly attached and can not easily rotate, and does not tend to flop downwards or slip like ring harnesses, as well as there being a wide variety of other devices the dildo style sex toys can be attached to, such as handles and inflatable balls. The disadvantage is the relatively low availability and high cost of compatible attachments. A number of brands have non-compatible clones of the vac-u-lock system, but dildos and accessories for them are virtually unavailable.
A recent design are strapless strap ons, designed to hold itself in a woman's vagina with an egg-shaped bulb, and does not require the use of a harness. This differs from a double dildo, in which both ends are symmetrical, as a double dildo can not hold itself in place in one partner while penetrating the other partner. The advantages of this design is that it can be used without any preparation, making using it much more spontaneous, that it provides deep internal thrusting to both partners, and that it can be more comfortable than having to wear a possibly bulky harness. However, it has the disadvantage that it may require strong muscles to use, and it may take practice to be comfortable with one.
Double dildos A double dildo can be used with or without a harness, although most provide no means of using them with a harness. A double dildo, as its name implies, is a dildo in which both ends are designed for insertion, and often is 18 inches or more long. While special ones meant for use with a harness do exist, a normal double dildo is straight, is rarely at a comfortable angle for intercourse, and jabs into the cervix of a woman using one. However, double dildos can be used for a variety of creative positions for which a harness would be awkward, such as both partners in doggy style positions or sitting facing each other.
Some harnesses and dildos are made of a single piece of molded latex, with the dildo permanently built into the front. These are often inexpensive, shoddy products, although higher quality ones are available. The advantages are simple use and an appearance some people find erotic, but this is often outweighed by the inability to use a different dildo, the often weak, floppy nature of the dildo, the inability to adjust to a given person for a comfortable fit, and their relatively short lifespan.
Straps directly attached to the dildo Some very cheap strap-on dildos have straps or attachments for straps directly molded into the material of the dildo. This design is very flimsy, and is only used on the cheapest of cheap products. They are essentially useless for the traditional purpose of a )strap-on dildo one partner penetrating another using a dildo in a position similar to a penis, but can be strapped around chairs and other objects for a variety of interesting activities.