seat belt/harness anchorage?

[JakeH]

evening all,

is there anything wrong with using m12 captives rather than 7/16ths stated in the book, had a quick gander at the iva manual thinggy and cant find anything relating to the thread or size of the bolt, what would you guys suggest?

Ta Very Much

JakeH

[David_17]

7/16th is standard for seatbelt mounting bolts. Why do you want to use M12s?

[JakeH]

7/16th is standard for seatbelt mounting bolts. Why do you want to use M12s?

just what iv got lying around, do you have to use specific bolts for the mounting points then? i know that seatbelt bolts are usually a coppery colour.

Ta Very Much

JakeH

[David_17]

Just high tensile ones. 8.8 or higher. Not sure about the thread though personally, which is why i went with the 7/16s

[ozzy1]

7/16 UNF(unified national fine) is the standard used.This is obviously a fine thread.You can also get UNC(unified coarse).There is a genuine reason for using a fine thread although i cant remember what it is/was.:eek:
Personally i would go for the 7/16 UNF or if you cant get them then go for M12 in a fine pitch,M12 by 1.50 pitch as opposed to the standard M12 by 1.75.Although probably easier to get the UNF thread than a metric fine.;)(8.8 tensile strength or 12.9)

[MarkB]

Most belts are supplied with fittings and they are always 7/16unf

[les g]

Ozzy
its something to do with fine threads are stronger and less likely to shear
its one of those clever/silly/nerdy techno equation things like shear stress and tensile strength stuff.
But 7/16 unf is not compulsory for iva you just have to have alternative fixings of adequate/ equal strength to 7/16 unf
But it is really easy to get hold a tap and the right drill bit for 7/16 unf
choice as they say is yours :D
HTH les g

[twinturbo]

Finer threads = more surface area = stronger.

TT

[flyerncle]

Makes lots of sense Les,every pitch is a potential fracture and the finer the better in engineering terms.

[MarkB]

Makes lots of sense Les,every pitch is a potential fracture and the finer the better in engineering terms.

That and for some odd reason belt firms still supply belts with 7/16 unf fittings rather than foreign millymetric stuff:)

[davidimurray]

If you plan on use plain m12 bolts you may need to sleeve the bolts to allow the harness brackets to roatate freely unless you plan on using eyes. My harnesses came complete with the 7/16 bolts and the sleeves.

[snapper]

The IVA tester will look for movement in the harness end, usually provided by the tophat washer and the wavy spring washer provide this.
Eye bolts and seatbelt clips are also acceptable and are generally metric coarse thread.

[David_17]

Just thought I'd mention, my IVA tester said m12 bolts are fine for seatbelts. So long as the length it ok.

He also mentioned, the roll bar doesn't have to be threaded, you can have the bolt going through a sleeve in the roll bar with a nyloc nut on the bottom.

[mistergrumpy]

I've used M12 on my Locost simply because it was free to me if I did it this way.
The one issue I have now is that the harness brackets don't rotate on the bolts and are captive and I had to widen the 7/16" holes in the brackets ever so slightly. None of this was an issue at SVA. The tester wasn't interested in the fact the belts were captive. However, I am and am looking for some way round it now without redoing the whole thing.

[MarkB]

I wouldn't alter the hole sizes on the belts, if they are supplied to suit 7/16 bolts then use 7/16 bolts...It might come back and bite yer arse if you ever needed to claim on insurance. Belts are a "safety thing" after all.

[mistergrumpy]

It might but then again it might not. I doubt they'd notice as it's only around 1mm bigger in the diameter, so 0.5mm off each side.