Nuts & Bolts - which type to use?

[Edin Dundee]

I'm familiar with UNF, UNC, Metric etc, and at work I use a variety of exotic materials - sometimes I know why, other times it's because that's what's fitted.
So on cars, what should be used?
I can get access to 316L stainless (sometimes known as A4) UNF and UNC nuts and bolts in some sizes - I know 316L stainless is highly resistant to corrosion, but I suspect it's also soft because of the low carbon content?
I see 'high tensile' bolts being suggested - what makes the things high tensile and how can you tell?
I use silver plated 316L bolts at work, I'm presuming the silver plate helps stop SS biting on itself?
I see cadmium plated bolts used in some places - what does cadmium bring to the equation?
On exhaust manifolds I'm assuming some special heat-resistant alloy is used for the studs and nuts?

Whatever happened to the penny washer? (it went metric, I know).

[MIG Wielder]

Hi Ed, I asked around here in the "mecchy" department and I got some answers as below.
Stainless steel bolts: Expensive; not high tensile so not for car suspension etc; and as you say reasonable corrosion resistance depending on the grade of stainless.
High tensile . The difference is "grade of steel" couldn't get more out of them on this. " 8.8 " marked on the head for high-tensile . Other markings are available !
Silver plated bolts. Now this is quite specialised. I recognised these. I imagine you work with high frequencies / R.F ?
The phrase about stainless not biting to itself wasn't known here.
Cadmium plating was banned some years ago now. Offers a degree of corrosion resistance. Cad; plating is toxic. They reckon these days that zinc is the "acceptable substitute".
Apparantly can be recognised by a rainbow colour effect (?) when clean and new.
Exhaust manifolds from personal experience: Brass nuts on mild steel studs work well. ( Old mini / MGB ) Stainless steel studs + "Aero-stiff" nuts ( Lotus)-the studs still work loose here and take the nuts with them.
My youngest's old Ford. Mild steel nuts; mild steel washers on mild steel studs. Horrible to work on.

Ah yes . Penny washers. Packs of 6 from B & Q. About 80p from last time i bought them.
A 2p piece is copper plated steel . And cheaper .
Do you have B & Q stores in Dundee ?

There are quite a few knowledgeable "nut-and-bolt" owners on here. They may still be on holiday this week though.

HTH,

Cheers for now,
Tony TDC 0091

[sprint95m]

I see 'high tensile' bolts being suggested - what makes the things high tensile and how can you tell?

Look at the bolt head. It should have a rating.
"S" indicates high tensile on UNF (look at the bolt head).
8.8 indicates high tensile on metric (and on some newer UNF too.) (I think the 8.8 is 8.8 MN per square metre?)

Stainless steel is OK for low load applications only.
Please use the correct rated bolts for all the suspension, steering, etc.
You can buy imperial fixings from agricultural, marine, HGV suppliers etc as well as car outlets.

[jikovron]

you can get metric bolts in 4.8 mild steel low tensile (but ideal for parts that suffer from vibration like alternators rocker covers door handles ect)

8.8 is med carbon tempered steel that has decent fatigue life so is suitable for shock loaded bits like suspension
10.9 and 12.9 are very high tensile strength bolts that have little fatigue life due to the hardness level so must NOT be fitted to the suspension (i used some on a shockabsorber mounting on another car and it snapped them within a few weeks due to fatigue)
14.9 bolt are in there own class and are only usefull for very high loaded parts that are precise fit like connecting rod bolts ect

imperial bolts usually have the strength level indicated by strips on the top of the hex head running radialy outwards so no strips is like a 4.8 mtric equivalent
3 radial strips would be like an 8.8
6 strips would be like a 10.9/12.9

there's also the most commonly found imperial grades R S T V which follow on in a similar way to metric