2 1/2 SQUARE KELLY 1.AISI 4145H modified alloy steel to API Spec7-1 2.drill pipe,drill collar,heavy weights, subs etc. SFMC 2 1/2 SQUARE KELLYs are made from AISI 4145H modified alloy steel in accordance with API Spec. 7-1 latest edition, which are quenched and tempered along full length. A hardnedd range of 285 to 341 BHN and a minimum impact value of 54 Joules as per ASTM A 370 Charpy-V, these ...