A center piece of a puzzle is a piece that only has one sticker and lies on only one face. On the 3x3x3 there are 6 centers, one for each color, which do not move. On larger cubes (such as the 4x4x4), however, there are many center pieces of many different types. Here is an illustration of all the types of centers:
The types of centers are the following:
- Fixed centers (or center-centers) are found at the very center of a face and do not move. These are not found on even cubes.
- X-centers are the centers which lie on the diagonals of the face of a cube puzzle. They get their name from the X shape they make on the faces of the puzzle if you also include the fixed center.
- T-centers (also known as plus-centers or +-centers) are the centers which are moved when you turn a middle slice. They get their name from the + shape they make on the faces of the puzzle if you also include the fixed center.
- Obliques are the centers which do not belong to any of the previous three groups. These centers have the interesting property that they cannot always be exchanged with each other - there is actually a set of 'left' obliques and a set of 'right' obliques which are mirror images of each other and cannot be placed in each others' spaces. Because of this, although there are 48 obliques of each shape, they are always separated into two orbits.