BS 6703:1988 download.British Standard Specification for Manually operated torque wrenches and drivers.
1 Scope
BS 6703 specifies requiremnts for the dimensions, design characteristics and operating effort for manually operated torque wrenches and drivers, in the 6.3 mm to 25 mm square drive range, used for control of the tightening torque of threaded fasteners. It also specifies requirements for endurance, torque value ranges and accuracy for the use of these hand tools.
2 Definition
For the purposes of BS 6703 the following definition applies.
parallax error. The apparent difference in reading when the scale and pointer are not viewed normal to the scale.
3 Classification
For the purposes of BS 6703 torque wrenches and drivers are classified as follows.
Type 1: indicating (see figure 1). Includes bending beam and dial wrenches (list number 258 In BS 6416) and dial indicating or electronic indicating wrenches and drivers.
Type 2: settIng (see figure 2). Includes graduated torque wrenches, click or slip type (list number 259 in BS 6416) and graduated torque drivers.
4 Finish
Exterior surfaces of torque wrenches and drivers shall be smoothly finished, eliminating sharp edges and corners capable of causing injury.
Parts subject to corrosion shalf be protected by methods In accordance with the appropriate British Standard,
e.g. BS 1706, BS 3597, BS 4232, BS 4641, BS 4758 and CP3012.
5 Drives
Drive squares shall comply with the dimensional and hardness requirements of BS 4006.
6 Maximum torque value
The maximum torque value for each square drive size of Individual torque wrenches and drivers shall be as given in table 1.
NOTE 1. IndIvidual torque wrenches and drivers have their own specific range.
NOTE 2. It Is recommended that the minimum torque value for a wrench or driver Is not less than 20 % of Its maximum torque value.
Table 1. Maximum torque values
7 Operating effort of torque wrenches
The force required to operate the torque wrenches to full torque value shall not exceed a force of 780 N applied to the centre of the hand grip.
8 Overload torque value excluding slip type wrenches and drivers
Each wrench or driver shall be capable of transmitting an amount 25 % in excess of its maximum torque value without physical failure, In both clockwise and anti- clockwise directions.
Non-reversible ratchet tools shall be overloaded In one dIrection only.
9 Parallax error
When viewed from an angle of 30 ° maximum to a line normal to the scale, the parallax error P• shall not exceed half the distance between the adjacent graduations on type 1 wrenches and drivers, or the distance between the adjacent graduations on type 2 wrenches and drivers. when calculated from the following equation:
P. tanaH where
a is the angle of view relative to a line normal to the scale (in degrees);
H Is the height of pointer above scale (in mm).
NOTE. For a viewing angle of
10 Accuracy
When tested in accordance with appendix A, the accuracy of wrenches and drivers shall be as follows.
(a) For the maximum torque value, the measured tolerance shall be not greater than ± 3 %.
(b) For the minimum torque value of 20 % or less of the maximum torque value, the measured tolerance shall be±6%.
NOTE. A minimum torque value of 20 % of the maximum torque value is recommended1 but a value of less than 20 % may be required for special purposes.
(c) For the mid-point of the maximum and minimum torque values, to the nearest graduation line, the measured tolerance shall be not greater than the tolerance calculated for the mid-point in accordance with A.2.
If any of the measurements carried out In accordance with appendix A do not comply with items (a), (b) and (c), the test shall be repeated. If, following a retest, any value still does not comply, the wrench or driver shall be deemed not to comply with this British Standard.
11 Endurance
11.1 Type 1 wrenches and drivers
When tested in accordance with B.2 and B.3, type 1
wrenches and drivers shall comply with clause 10.
11.2 Type 2 wrenches and drivers
When tested in accordance with B.2, B.3 and B.4, type 2
wrenches and drivers shall comply with clause 10.
12 Safety and instructions
The following guidance on the correct and safe use of torque wrenches and drivers shall be included with the instructions.
(a) Never overadjust the wrench or driver by exceeding the maximum adjustment, which is indicated.
(b) Do not snatch the wrench or driver when tightening but apply a smooth, continuous pull.
(c) Adopt a firm stance when using the wrench or driver in case the tool slips.
(d) Do not use the wrench or driver outside its maximum capacity, e.g. as a lever for undoing seized nuts where the torque required is in excess of the torque value of the torque wrench.
(e) Inspect the wrench or driver periodically to ensure that the parts are in good order.
(f) Follow the manufacturer’s instructions with regard to care and maintenance.
(g) Follow the job application Instructions with regard to lubrication, condition of threads and tightening
sequences.
(h) Periodically check for calibration wrenches or drivers that are In frequent or continuous use.
NOTE 1. Reputable manufacturers will normally offer a calibration and repair service.
NOTE 2. Manufacturers’ instructions should cover the following points:
(a) correct selection of the tool for application;
(b) method of use of tool;
(c) care and maintenance of tool;
(d) Information as to where to obtain further advice.
13 Marking
The wrenches and drivers shall be marked In a legible and permanent manner with the following information:
(a) the manufacturer’s or vendor’s name or trademark;
(b) the units of measurement, i.e. Nm;
(c) the direction of torque measurement for tools that
operate in one direction only.
Wrenches and drivers or their packaging shall be marked with the number and date of BS 6703, i.e. BS 6703: 1988.