WORLDWIDE FASTENER STANDARD
WE954 Date: 2007-03-01
General Specifications, Assembly Information, Mechanical and Performance Requirements for ISO Metric
Threaded Spring Nuts
Foreword:
Update 2007 March 1st
During the March 1st, 2007 update the only change was a cautionary not added to the Scope stating:
Nuts of size M10 and larger are unsuitable for ‘clamp load critical’ applications.
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WORLDWIDE FASTENER STANDARD
WE954 Date: 2007-03-01
General Specifications, Assembly Information, Mechanical and Performance Requirements for ISO Metric
Threaded Spring Nuts
1. SCOPE. This standard covers material, heat treatment, and performance of ISO metric threaded spring nuts, in
the range M4 to M12 inclusive.
NOTE: The design may vary between manufacturers provided all requirements of this standard are met. Nuts of size
M10 and larger are unsuitable for ‘clamp load critical’ applications.
1.1 REFERENCES
ISO 261 - General purpose metric screw threads - General plan.
ISO 683/18 Heat-treated steels, alloy steels and free cutting steels-Part 18: Wrought unalloyed steels in
the normalized, or normalized and cold-drawn, or hot-rolled and cold-drawn condition.
ISO 898-2 - Mechanical properties of fasteners
ISO 965-2 - General purpose metric screw threads - Tolerances.
WSD-M1A283 (B37/B38/B39/B50/B52) Steel, cross reference standard parts.
W-HTX - Control of Heat Treating Processes and Auxiliary Equipment
2. MATERIAL AND HEAT TREATMENT
2.1 MATERIAL. The material shall be spring steel in accordance with WSD-M1A283-B37/B38/B39/B50/B52.
2.2 HEAT TREATMENT. Austemper to HV420 - 520, Process tests and controls per W-HTX.
2.3 IDENTIFICATION. Spring nuts shall be permanently and legibly marked with manufacturer's identification.
2.4 THREADS Threads in the extruded barrel shall be roll forming only and shall conform to the basic
dimensions and Class 6H tolerances for internal metric screw threads in accordance with ISO 261 and ISO
965/2.
2.5 RETAINING EXTRUSION. Retainer formed width shall not exceed the minimum panel hole diameter as
specified in Table 1. Retainer bottom leg clearance shall not exceed minimum panel thickness as specified
in Table 1 and Figure 1.
2.6 WORKMANSHIP. Nuts shall be free from cracks, splits, burrs, loose scale and any defect(s) that affect fit,
form, or function.
2.7 PROPRIETARY VARIATIONS. Design of retaining feature(s) and other dimensional details of parts
produced by individual manufacturers may vary within envelope dimensions given, provided all
requirements of this specification are met.
3. PERFORMANCE.
3.1 INSTALLATION. Spring nuts shall be designed to minimize required installation force to application panels.
As applications vary considerably, maximum installation force specification shall be designated by
individual spring nut design releases. Forces for installation shall be 55N maximum for 6mm and smaller
spring nuts, and 90N maximum for 8mm through 12mm sizes on the following installation force test panel:
Unless otherwise specified, installation force test panels shall be constructed of WSD-M1A283-B52 or
equivalent steel, smooth (Ra 2.5μm) hardened to HV613-653, have a thickness of the maximum
application panel, and have an edge radius per Table 2. Installation forces shall be applied at a travel rate
of 4 ± 1mm/second via a testing setup per Figure 2.
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WORLDWIDE FASTENER STANDARD
WE954 Date: 2007-03-01
3.2 RETENTION. Spring nuts shall be assembled onto test panels of the specified minimum application panel
thickness, having minimum diameter holes located at their maximum recommended edge distance, per
Table 1. The retaining feature shall locate in the hole and pull force of 13N minimum shall be required to
remove the nut from the test panel. Pull forces shall be applied through the throat area of the nut and at a
travel rate of 4 ± 1mm/second via a testing setup per Figure 3.
3.3 STRENGTH. Spring nuts shall be prepared for testing by removing the lower leg and fold portion at the
rear as depicted by Figure 4. The nut, along with its test bushings, shall be assembled to the test bolt
(Figure 4) then installed to a tension test fixture. Test bushing shall be hardened to HV674-746 and
conform to dimensions shown in Table 3. Load shall be applied at a maximum travel rate of 25mm/minute.
3.3.1 SLEEVE HEIGHT DEFORMATION. The actual sleeve height "A" (Figure 1) shall be measured
and recorded. The leg containing the threaded extrusion shall be assembled onto the test bolt, as
shown in Figure 4, then installed into a suitable tension test fixture. A tension load shall be applied
to this assembly equal to the value shown in Table 4 for the appropriate thread diameter. Once
this load is obtained, the load shall be released, the test bolt removed, and dimension "A" recorded
again. The maximum permanent sleeve height set is obtained by subtracting the original sleeve
height dimension from the final sleeve height dimension. This amount may not exceed the value
specified in Table 4.
3.3.2a PROOF LOAD, FREE-RUNNING SPRING NUTS. A tension load equal to the proof load specified
by Table 5 shall be applied to the spring nut through the test bolt. The nut shall resist this proof
load without failure by rupture, collapse, cracking, or thread stripping, and the test bolt shall be
removable from the nut by the fingers after the proof load is released.
(NOTE: Occasionally it may be necessary to use a manual wrench or other means to start the
bolt's motion. Use of such means is permissible provided the bolt is removable by the fingers
following initial loosening of not more than one-half turn of the bolt.)
3.3.2b PROOF LOAD, PREVAILING TORQUE SPRING NUTS. A tension load equal to the proof load
specified by Table 5 shall be applied to the spring nut through the test bolt. The nut shall resist this
proof load without failure by rupture, collapse, cracking, or thread stripping. The test bolt shall be
removable from the nut with a torque not to exceed the specified maximum first-on value.
3.4 TEST BOLTS. Test bolts shall be of ISO metric coarse thread form as specified in ISO 261 and ISO 965
and shall be Property Class 12.9. Test bolts shall be surface coated with any suitable finish and the thread
shall meet the requirements of a 6g tolerance class after coating.
Figure 1
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WORLDWIDE FASTENER STANDARD
WE954 Date: 2007-03-01
Table 1. Test panel
Nominal thread size Min. test panel thickness Min. test panel hole dia. Test panel edge distance to hole
(mm) ± .13mm ± .25mm ± .25mm Max
M4 0.60 7.5
M5 0.60 8.3 0.75 * B
M6 0.80 9.9 Where B is the
M8 0.80 11.3 throat depth
M10 1.50 14.7 of the spring nut
M12 1.50 17.3 (FIG. 1)
Figure 2 INSTALLATION FORCE
Table 2
Test Panel Thickness (mm) Test Panel Edge Radius (mm)
0.600 - 1.139 0.13 - 0.25
1.140 - 2.999 0.25 - 0.51
3.000 - 8.500 0.76 - 1.27
Figure 3 RETENTION FORCE
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WORLDWIDE FASTENER STANDARD
WE954 Date: 2007-03-01
Test Bushing and Table 3
Figure 4
Table 4
Nominal thread Size Permanent set Permanent set
(mm) Tensions test load (kN) Allowed max (mm)
M4 5250 0.25
M5 9110 0.25
M6 12900 0.38
M8 23850 0.51
M10 37540 0.64
M12 55650 0.76
Table 5
Nominal thread Size Proof load - min
(mm) (N) + 1%/-0
M4 7000
M5 12140
M6 17200
M8 31800
M10 50050
M12 74200
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WORLDWIDE FASTENER STANDARD
WE954 Date: 2007-03-01
Recommended Assembly Data
Nut Size Style A B C D E F
Edge Panel Hole Nut Slot or Emboss Emboss
Distance Diameter Length Emboss Depth Depth
Clearance Width
Max Min Max Min Min1 Max Min Min1 Min1
M4x0.7 Short 9.0 8.0 8.3 7.5 18.0 15.0 14.0 2.5 1.0
Long 13.0 12.0 23.0
M5x0.8 Short 10.5 9.5 9.1 8.3 20.5 16.0 15.0 2.5 1.1
Long 15.5 14.5 26.5
M6x1 Short 12.5 11.5 10.7 9.9 25.0 16.5 15.5 2.5 1.2
Long 18.5 17.5 31.5
M8x1.25 Short 13.5 12.5 12.1 11.3 26.5 20.0 19.0 2.5 1.4
Long 20.0 19.0 33.5
M10x1.5 Short 17.5 16.5 15.5 14.7 35.0 26.0 25.0 3.0 2.0
Long 27.5 26.5 45.0
M12x1.7 Short 22.5 21.5 18.3 17.3 43.5 33.0 32.0 3.2 2.2
5
Long 32.5 31.5 53.5
1
Consideration should be given to tolerance of manufacturing practices used to emboss and punch these features
when designing panels in which they are employed.
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