Aikido Uniforms and Ranking Aikido practitioners (commonly called aikid?ka outside Japan) generally progress by promotion through a series of "grades" (ky?), followed by a series of "degrees" (dan), pursuant to formal testing procedures. Some aikido organizations use belts to distinguish practitioners' grades, often simply white and black belts to distinguish kyu and dan grades, though some use various belt colors. Testing requirements vary, so a particular rank in one organization is not comparable or interchangeable with the rank of another. Some dojos do not allow students to take the test to obtain a dan rank unless they are 16 or older. The uniform worn for practicing aikido (aikid?gi) is similar to the training uniform (keikogi) used in most other modern martial arts; simple trousers and a wraparound jacket, usually white. Both thick ("judo-style"), and thin ("karate-style") cotton tops are used. Aikido-specific tops are available with shorter sleeves which reach to just below the elbow. Most aikido systems add a pair of wide pleated black or indigo trousers called a hakama (used also in kendo and iaido). In many schools, its use is reserved for practitioners with (dan) ranks or for instructors, while others allow all practitioners to wear a hakama regardless of rank.