12. 15. Bored hole size before tapping ( for thread cutting ) ■ for Unified Threads Unit : mm Production data Size Minor diameter of internal threads (D1) Bored hole size Size Minor diameter of internal threads (D1) Bored hole size ( ref.) ( ref.) 1.27 13.8 1.54 14.60 1.58 14.92 1.83 16.7 1.87 17.59 2.09 17.89 2.15 19.6 2.33 20.6 2.41 21.06 2.64 22.5 2.69 23.5 2.83 S 23.7 2.97 24.24 3.47 25.2 3.55 25.6 10 3.89 26.6 10 4.12 27.30 12 4.53 28.4 12 4.67 28.8 12 4.78 29.8 5.19 30.47 5.53 30.9 5.64 32.0 16 6.65 33.0 16 6.97 33.65 16 7.22 34.1 8.07 35.2 8.57 36.2 8.81 36.82 16 9.5 38.3 16 9.96 39.3 16 10.29 40.00 10.9 39.6 11.54 41.5 11.88 42.5 16 12.3 4.5 45.4 16 13.00 47.9 16 13.32 48.9 • The recommended tap drill sizes indicated above are for ANSI B1.1 Class 2B UNC, UNF, UNEF, UN & UNS threads. Information Technical Technical-38 809