Kellys Kellys is driving section of wohole drill stem. Kelly is available with square kelly and hexagonal kelly. TIANHE brand kelly are manufactured strictly from API Spec7-1 and SY/T6509-2000 standard. Technical specification and parameters Size in Upper box connection Lower pin connection I.D.(mm) Driving section (mm) Connection (LH) O.D.(mm) Connection (LH) Square Hexagonal Cross flat For square kelly Cross corner for hexa kelly Std Optional Std Optional Square O.D. (mm) Hexagonal O.D. (mm) 2 1/2 6 5/8REG 4 1/2REG 196.8 146.0 NC26 85.7 31.8 63.5 83.3 3 6 5/8REG 4 1/2REG 196.8 146.0 NC31 104.8 NC26 85.7 44.4 31.8 76.2 100.0 85.7 3 1/2 6 5/8REG 4 1/2REG 196.8 146.0 NC38 120.6 NC31 104.8 57.2 44.4 88.9 115.1 100.8 4 1/4 6 5/8REG 4 1/2REG 196.8 146.0 NC46 158.8 NC38 120.6 71.4 57.2 108.0 141.3 122.2 6 5/8REG 4 1/2REG 196.8 146.0 NC50 161.9 NC38 120.6 71.4 57.2 108.0 141.3 122.2 5 1/4 6 5/8REG 196.8 5 1/2FH 177.8 NC46 158.8 82.6 76.2 133.3 175.4 151.6 6 5/8REG 196.8 NC56 177.8 NC50 161.9 82.6 82.6 133.3 175.4 151.6 6 6 5/8REG 196.8 5 1/2FH 177.8 88.9 152.4 173 6 5/8REG 196.8 NC56 177.8 88.9 152.4 173 All technical specifications and parameters only provides for reference.