HHG, H 級精度為參考TAS 規格設定,經研磨加工之螺絲攻依其階段等級,均可適用於 JIS 2 級或同等以上之精度。絲攻有效徑公差區域如下所記。
HHG, H grade system for thread limits is specified in reference with TAS (The Japan small tool makers association standard), most of the HHG ground finished taps use this limit system, on pitch diameter tolerance zone for pitch size are as follows.

螺 距 Pitch

有效徑公差 Pitch dia tolerance

1. P≦0.6 (40山以上) P≦0.6(T.P.I≧40)

15 µm

2. P≧0.7 (36山以下) P≧0.7(T.P.I≦36)

20 µm