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
| 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. | ||||||||
