The UY 321 STAY needle has a stay point. It is used in special sewing machines for inserting reinforcement tape (stayband). Suitable machine classes are found, among others, at Union Special (classes 3000, 9500 D, 10600 L, 11500 A, K), Mauser (classes AA, ABG, AE, AHF) and Singer (classes 62, 106, 109, 147).
Thinner needle sizes are used, among others, for light applications of reinforcement-tape insertion, and the thicker versions for heavy applications of reinforcement-tape insertion. As sewing thread, a strong polyester thread such as Amann Serafil or Rasant is usually recommended, in a thickness matching the needle size chosen.