Despite its small size this is one piece of Pilates equipment that can really pack a punch. It used to be called the spine corrector. It has a padded upholstered wooden arc with a ledge or step surface attached to it. You will also find handholds attached to the side. These handholds help keep the body stable. You may also see this piece of kit referred to as a step barrel.
The purpose of the curved surface is that you have to work with an incline or a decline which creates a different challenge to exercising on a Pilates mat. This allows you to target your hips, shoulders and spine in a different way.
You can use the arc either as a stand -alone piece of kit or in can be used together with other Pilates equipment like the Cadillac and reformer. In fact with the reformer it can help provide more variation and can provide more back support and stability.
There are a number of different arc designs on the market.
The first thing to be aware of is that the curves are more acute in some arcs than others. Taller users will benefit from an arc that has a more elongated curve. Some arcs also have shallower steps, here your height will be crucial.
Check the upholstery which can also vary. Ideally you want to have an easy to wipe and keep clean cover - especially if it's for a studio environment.
Construction can also vary between manufacturers, ideally look for a sturdy wood construction that uses a marine or birch play. THis adds flexibility to the wood, as well as strength.
If you want the arc to fit onto existing Pilates equipment then make sure they are compatible. For example some arcs have been especially designed to fit over a reformers shoulder rests.
Also check what storage space you have to ensure it will fit into your home. Some arcs can also be flipped over and used curved side down.