圆角处理，厚度约0.8mm，符合NEMA标准。
      锌板通常用于确定研磨砂条如S-42的磨耗速率。
      S-34锌板每面研磨次数不得超过十次。
      S-34 Zinc Standardization Plates are used to evaluate the abrasion characteristics of S-42 and S-33 sandpaper strips. Each plate is 4” square, .032” zinc with ¼” center hole. (5 pcs.)