Body Jewellery Screw-fit add-on's. These are threaded accessories such as gem balls which can be screwed on to the end of Bars, Studs and Horseshoes. We have a variety of different types of add-on's such as cones, stars, spikes, gem balls, plain balls. Having a variety of add-on's gives you the ability to change the look of your jewellery without removing it from the Piercing. Screw-fit Add-on's come in different gauges and the gauge of the add-on should match the gauge of the body jewellery. For more information about sizing please read our guide. There are two types of threading for screw-fit add-on's, Internal and External. Externally threaded add-on's are the most common and have the thread on the bar or stud, this fits inside the ball or cone, and screws on and off. Internally threaded add-on's are usually used in Dermal Anchors and Labret Studs, the threading sticks out of the ball and this fits into tube on the internally threaded body jewellery.