Personalized Intelligent Triangle Light Youth Long Sleeve T-Shirt. Triangle with the letter A in the word triangle replaced with a percussion triangle with text, the instrument for intelligent people, is a funny gift design with attitude for percussionists, music teachers and students in orchestra and concert band. youth long sleeve t-shirt. Shoulder-to-shoulder taping. Youth: S(6/8), M(10/12), L(14/16), XL(18/20)