• A hexagon key is an internal wrenching tool used to tighten hexagon socket head fasteners and set screws. In this article information about care to be taken while using hexagon keys and manufacturing standards is given.

    Care to be taken while using hexagon keys

    Always ensure to use snug fit keys having full wall contact to get desired tightening torque. A worn out key will slip in the socket and may damage it making it useless to tighten later to required torque even with a good key. A good quality key has high strength and ductility. With a good quality key, far more tightening torque than is needed can be applied without damaging the screw or the key. A good quality key shall twist and shear off clean with out damaging socket when excessively tightened (destruction test). Please remember that cost of a key is negligible as compared to problems one may face later due to bad workmanship due to use of a bad key.

    As a thumb rule, a fastener will get adequately tightened when the short arm is inserted in the socket and the long arm is deflected or bent through an angle of 25-30 degrees by the application of force near the end of the long arm.

    Product and dimensions standards

    Product and dimensions standards used for hexagon key in various countries are as under.

    ANSI: B 18.3, B 18.3.2M
    IS: 3082
    ISO: 2936
    DIN: 911
    BS: 2470

    For ready reference, information on metric hexagon keys made by Unbrako as per ANSI standard from their engineering guide is reproduced below.

    Metric Hexagon Keys – Dimensions and Mechanical Properties

     

    Hexagon Key

     

     

    key size W B nominal C nominal Torsional shear strength minimum Torsional yield strength minimum
    max. min. short arm long arm N-m In-lbs. N-m In-lbs.
    0.711 0.698 5.5 31 69 0.12 1.1 0.1 0.9
    0.889 0.876 9 31 71 0.26 2.3 0.23 2.
    1.270 1.244 13.5 42 75 0.73 6.5 0.63 5.6
    1.500 1.470 14 45 78 1.19 10.5 1.02 9.
    2.000 1.970 16 50 83 2.9 26 2.4 21
    2.500 2.470 18 56 90 5.4 48 4.4 39
    3.000 2.960 20 63 100 9.3 82 8. 71
    4.000 3.960 25 70 106 22.2 196 18.8 166
    5.000 4.960 28 80 118 42.7 378 36.8 326
    6.000 5.960 32 90 140 74 655 64 566
    8.000 7.950 36 100 160 183 1,620 158 1,400
    10.000 9.950 40 112 170 345 3,050 296 2,620
    12.000 11.950 45 125 212 634 5,610 546 4,830
    14.000 13.930 55 140 236 945 8,360 813 7,200
    17.000 16.930 60 160 250 1,690 15,000 1,450 12,800
    19.000 18.930 70 180 280 2,360 20,900 2,030 18,000
    22.000 21.930 80 200 335 3,670 32,500 3,160 28,000
    24.000 23.930 90 224 375 4,140 36,600 3,560 31,500
    27.000 26.820 100 250 500 5,870 51,900 5,050 44,700
    32.000 31.820 125 315 630 8,320 73,600 7,150 63,300
    36.000 35.820 140 355 710 11,800 104,000 10,200 90,300
    All dimensions in millimeters.

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