Thread: Bolt strength for stupid people

Originally Posted by Dougal

A 10mm bolt in double shear is stronger than a 12mm in single shear. But it's a situation not relevant to the original topic.

You stated:

Originally Posted by Dougal

...

Put simply, 10mm bolts are rubbish and can never be safe.

A single 10 mm bolt in double shear is the same (theoretical) strength as the OP's situation of 2x 10 mm bolts in single shear. Plus with a Jate ring design there is no guarantee you are applying loads evenly.

Originally Posted by isuzurover

You stated:


A single 10 mm bolt in double shear is the same (theoretical) strength as the OP's situation of 2x 10 mm bolts in single shear. Plus with a Jate ring design there is no guarantee you are applying loads evenly.

The first situation is a bolted joint. For the joint to perform properly and protect the bolts they must not slip.
For this purpose at the "rated" load 2xM10 bolts are insufficient.

Jate rings (which I have never used and likely never will) are not a bolted joint. They are not using friction to carry the load and protect the bolts.

Personally, I don't think there are any way of confirming any recovery point, for every situation. As I mentioned before, the actual recovery point, weather it be a hook, plate, or ring. You would probably find that the mounting point to the chassis would fail before anything else. Even with my dodgy 4.8 bolts through my rated hooks, I would expect something else to fail before the bolts. The time I loaded up both hooks, I would be looking at 7.6 ton, that type of weight dragging the front end out, I'd expect something to let go.
Anyway, I was given a refund, I still need to buy some new bolts, and they said they would look into it.
I don't really expect them to change anything, but hopefully it will come to light for anyone who has the same issue without causing damage or injury.

Originally Posted by blindin

Personally, I don't think there are any way of confirming any recovery point, for every situation.

Not for every situation, but applying a safe load rating to lifting points and supporting structure is a service my company provides. The situations the rating applies to is always set-out.
There are things flown around under helicopters by attachments I've designed and certified.

Recovery points are little different, certainly no more difficult and the major difference is the lack of published standards and codes.
I've already given you a bolt and attachment spec in this thread that will withstand more ~4,500kg recovery load cycles than any individual operator will.

Originally Posted by blindin

As I mentioned before, the actual recovery point, weather it be a hook, plate, or ring. You would probably find that the mounting point to the chassis would fail before anything else. Even with my dodgy 4.8 bolts through my rated hooks, I would expect something else to fail before the bolts.

See my earlier comments about the crush-tubes and bolt sizes required. If you use grade 4.8 M10 bolts then they'll move, slog the holes out, damage the bolts and eventually destroy the mounts.
This is failure caused by the fastener choice.

I will defiantly be changing out the bolts, just haven't done it yet.
The problem with 4x4 recovery equipment is that it is not governed, nor is it legal to have any of the equipment tested. If there were more regulation where would you start with it. There are to many factors which could change.
Not to mention the actual weight your trying to shift.
Most people think it going to weigh the weight of the car, but the true force can be 5 times more after taking into account the resistance. Unfortunately there is a very big grey area when it come to this in regards to recovery stuff.
Anyway, thanks for the help, I've made the company aware of the situation, and also know that I need to change out my bolts.

I found these in my travels - a list of bolt tensile strengths and shear capacity:

Newcastle High Tensile Bolt Company :Home Page
Newcastle High Tensile Bolt Company :Home Page

One tonne is basically ten KN (yeah I know it isn't exactly, but close enough)

And an interesting read re the real forces involved in recovery and snatching situations:

Pirate4x4.Com - Extreme Four Wheel Drive

Lots of misinformation in this thread.

One tonne is 10kN (9.81 if you want to be precise)

As far as I am aware there are no joints in vehicles generally that rely on friction between the fastened parts generated by the tension in the bolts to resist shear across the joint. High Strength Friction Grip joints are normally only used in structural steelwork and tend to involve many bolts and specific preparation of the faying surfaces to ensure the correct coefficient of resistance. These joints rely accurate torque in the bolts to generate the correct tension, normally achieved by using load indicating washers.

Lesser joints in structural steelwork just use bolts in single shear or double shear and are not torqued to specific torque just done up tight enough not to come undone.

Most bolted joints in vehicles are torqued to ensure even application of load to ensure that gaskets seal, (cylinder head) to ensure they are tight enough to prevent them coming undone through vibration or thermal cycling, or to prevent them being done up so tight that the bolt fails, or he thread into which it is screwed is stripped (water pump bolts into alloy block).

G4.6 bolts have no place on a vehicle other than for bolting non structural items like bits of trim or cable brackets.

Minimum of G8.8 for anything that has force applied to it or if it broke would make it a bad day.

10.9 where recommended by the WSM or maybe other stuff subject to unknown loads like recovery hooks.
But for a recovery hook through chassis plates 4mm thick a larger diameter G8.8 would be better as the chassis plate thickness would be the limiting factor in the strength of the joint.

12.9 only where specifically called for. Often used to hold break calipers together.

Originally Posted by jonse

As far as I am aware there are no joints in vehicles generally that rely on friction between the fastened parts generated by the tension in the bolts to resist shear across the joint.

You are completely wrong. Every bolted joint in your vehicle relies on friction to hold fastened parts together.

If you don't believe me, go loosen some of the less critical ones and go for a drive. Even your dash-board is held down by friction. Loosen the screws and you'll feel it slide around.

Originally Posted by jonse

High Strength Friction Grip joints are normally only used in structural steelwork and tend to involve many bolts and specific preparation of the faying surfaces to ensure the correct coefficient of resistance. These joints rely accurate torque in the bolts to generate the correct tension, normally achieved by using load indicating washers.

That is an extremely intensive bolt joint only used in special circumstances. I personally have never heard of any such joint being used in practice. They are that rare.

Normal joints are bolted up tight. Checked with a torque wrench if the Engineer asks.

Originally Posted by jonse

Lesser joints in structural steelwork just use bolts in single shear or double shear and are not torqued to specific torque just done up tight enough not to come undone.

All joints in structural steelwork are clearance. Usually 2mm minimum. This is to ensure there is no shear load on the bolts. The load is carried in shear by friction on the surfaces.
Your assertion that bolts are just done up tight enough to not come loose is wrong and extremely dangerous if anyone were to do that.

Originally Posted by jonse

10.9 where recommended by the WSM or maybe other stuff subject to unknown loads like recovery hooks.
But for a recovery hook through chassis plates 4mm thick a larger diameter G8.8 would be better as the chassis plate thickness would be the limiting factor in the strength of the joint.

This is also wrong. You should never be loading the bolts or the holes in shear in normal operation.
The limit on strength of a bolted join is the friction it generates. If a bolted joint slips. Then it has failed.