The Kegel exerciser is a medical device designed to be used by women to exercise the pubococcygeus muscle (also called the PC muscle). Men have no known methods of adding resistance to Kegel exercise as there is no method of inserting such devices without dangerous surgery.
There are three main types: barbells, springs, and rubber bulbs.
The barbells (or vaginal barbell) can be used as a vaginal exerciser or as a vaginal dildo or sex toy. Made of smooth, polished solid stainless steel, it is cylindrical in shape, with a rounded bulge at each end. They typically weigh one pound and measure approximately 6 3/4 inches (17.1 cm) in length with a diameter of one inch (2.5 cm) at the widest part. Being made of stainless steel, vaginal barbells are nonporous and can be wiped clean with a cloth moistened with mild soap and water. Because they do not have a flared base, they should not be used as an anal dildo as there is no way to prevent them from slipping inside.
Spring devices are made of plastic, with removable springs to allow progressive resistance. These allow pressing directly against resistance, and go by brand names like Pelvic Toner, iKegelPro, FeminX or KegelMaster.
An advantage of rubber bulb devices is that they provide visual feedback (via a gauge) of how much pressure you are applying.