VW T4, why fine thread bolts?

[dubwarrior2]

Ive just removed the rear suspension arms on my VW T4.
They pivot on m14x1.5 and m16x 1.5mm bolts which I'm going to replace.
Ive priced them up on the brickwerks site and they are pricey. I can get them cheaper on ebay.
The question is, in the description, it says to use fine thread bolts not normal pitch because "VW used fine thread for a reason".....
Really? What reason?
Id have thought normal thread would be ok. They both have the same diameter. And surely part threads would be better too.
Any ideas?

[kevins]

There would be 2 main reasons,

- you get more clamp load for a given torque with a fine pitch bolt.(it would have to be a high grade bolt as well)
- too make sure the wrong part can't be used in production, typically a manufacturer will use a fine pitch for all its 10.9 grade fastners to make sure they can't get mixed up with the 8.8.

Of more importance then the thread pitch is the getting right grade of bolt.

[dubwarrior2]

Yeah I appreciate the importance of the tensile grade.
They are torqued to 160nm.....so I'm sure a wider pitch could handle it. Either way I'll replace like for like

[chris y]

As kevins said, you get a lot more clamping load from the same torque, more precise clamping force too and less tendency to loosen.

[slater]

A finer thread is stronger. Think about it. The minimum diameter of a m16x2 is smaller than and M16x1.5


I'm not sure that really matters in this case tho!

[welshpug]

www.nord-lock.com/insights/bolting-tips/2010/choose-fine-or-coarse-thread-bolts/


found this on google, all makes sense and confirms the comments above.

[luckyseven]

Seems a bit overkill... you ought to be able to hang a decent-sized boat from the ceiling using even a "normal" M16 bolt and expect it to hold

[welshpug]

well its a rear suspension arm on a 2.8 ton van, so the loads are not insignificant.

[dubwarrior2]

Thanks all. On anything else I probably wouldnt be overly fussed, but on the suspension I'll copy the originals. I'll also use nylocs, which VW didnt