Fracture Load

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Please note: The highest permissible load is the minimum of static capacity C_0a (to prevent brinelling) and fracture load (to prevent failure of ball nut or bolts). Necessary condition for both is proper alignment and squareness of the mounting surfaces and also concentric applied load.

Additional limitations (e.g. buckling) may apply!

Nominal diameter [mm]	DIN 69051 bolt pattern	Dynamic bolt tension Fb* [kN]	Static bolt tension Fb* [kN]	Bolt torque [Nm]	Standard nut Maximum permissible axial load [kN]	UltraThrust nut Maximum permissible axial load [kN]
5/6	4xM3	5	20	1,5	C_0a	-
8	4xM3	5	20	1,5	C_0a	-
10	4xM4	7	28	3	C_0a	-
12	4xM4	7	28	3	7	-
16	6xM5	12	40	6	12	-
20	6xM6	16	63	10	16	-
25	6xM6	16	63	10	16	-
32	6xM8	32	100	25	32	-
40	8xM8	40	150	25	40	-
50	8xM10	80	225	49	80	120
60/63	8xM10	80	225	49	80	180
80	8xM12	125	320	86	125	200
100	8xM12	125	320	86	125	200-250
100	8xM16	250	630	210	250	250
125	8xM16	250	630	210	150¹	300
125	8xM16	250	630	210	250²	350

[1] Flange 25 mm thick
[2] Flange 30 mm thick
* Bolts DIN ISO 4762, Strength 8.8
(90% load, safety factor 0,8, µ = 0,14)

Technical Tip

The structural strength of ball screws for aerospace applications is first predicted using analytical methods including FEM analysis. In some cases, tests are performed in the development phase to demonstrate safety and avoid costly and time consuming redesigns once the qualification phase of the project has started.

For the final qualification, tests under exactly the same conditions as in the aircraft must be passed. These tests often require test rigs specific to the aircraft program, called "iron bird". The documentation of these tests becomes part of the aircraft qualification.

In addition to static tests (limit load, ultimate load), fatigue tests are conducted. In these fatigue tests, an alternating or pulsating load is applied to a ball screw that is not operating. This is not to be confused with endurance tests, which aim at fatigue also (to confirm dynamic load capacity), but with the pulsating load generated by balls running repetitively over the same spot of the ball track.