After arriving home from holiday with my caravan, I discovered that one of the two high tensile steel bolts that attach the coupling head to the caravan drawtube had sheared. The sheared bolt was still held in place by the rubber boot and the bolt head was stamped 10.9 (high tensile steel grade).
On investigation I have been told by a local caravan dealer that they only fit high tensile steel bolts grade 8.8 (lower tensile & yield) and have never heard of one of these bolts failing in the past.
As the grade 10.9 has a higher tensile and yield rating than the 8.8 it's a bit worrying why this failed.
I have found the following specifications:
8.8 grade = tensile 800 N/mm2, yield 640 N/mm2
10.9 grade = tensile 1040 N/mm2, yield 940 N/mm2
Is there something that I'm overlooking ? Could it be that some other factor makes 10.9 grade unsuitable for this application?
Your opinion would be greatly appreciated.
On investigation I have been told by a local caravan dealer that they only fit high tensile steel bolts grade 8.8 (lower tensile & yield) and have never heard of one of these bolts failing in the past.
As the grade 10.9 has a higher tensile and yield rating than the 8.8 it's a bit worrying why this failed.
I have found the following specifications:
8.8 grade = tensile 800 N/mm2, yield 640 N/mm2
10.9 grade = tensile 1040 N/mm2, yield 940 N/mm2
Is there something that I'm overlooking ? Could it be that some other factor makes 10.9 grade unsuitable for this application?
Your opinion would be greatly appreciated.