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The most noticeable feature of any strap on setup is the dildo used. A wide variety of dildos are available, and while the choices may be limited by the type of harness in use, generally one can chose from several common types. This section discusses the shape and features of the penetrating end of the strap on dildos, not of the entire dildo or how it's attached, which can be found in the section on dildo attachment methods for the double dildo and strapless dildo.
The "standard" dildo has a non-tapered or slightly tapered shaft, and often has an enlarged head, similar to a penis. The shaft may be slightly curved, but if it is strongly curved, it is often classified as a g-spot/prostate dildo as well. This type is by far the most popular, both for vaginal and anal use, although some beginners prefer a probe type dildo. Depending on the type of harness the dildo is meant for, it may have molded testicles as part of the base, which many people say gives more pleasure and helps keep the dildos from "bottoming out." Standard dildos are the most common by a large margin, and are available in virtually any length and width, material, texture, etc.
A probe dildo is often highly tapered, and many resemble a cone in overall shape, or may have a narrow diameter its entire length, although ones resembling an elongated butt plug are also common, their defining feature being a bulb in the middle which tapers down again towards the harness before flaring wider. These dildos are often advertised as being for beginners, especially newcomers to pegging, who may find a narrow, tapered dildo easier to start with if they've never had anal penetration before. Many people find that once they're familiar with the activity, the probe dildos are inadequate and unsatisfying, and purchase a standard dildo to use with their harness. Due to this, many kits include both a probe dildo and a standard dildo, so it's not necessary to purchase additional sex toys.