Classic cars forum & vehicle restoration.

ukdave2002 · Joined: 23 Nov 2007 Posts: 4240 Location: South Cheshire

I came across these 5/16 UNF bolts in a load of Triumph stuff.

The narrow waist at the tip suggests mass production self alignment , the spire relief in the thread suggests self cutting....They are however only mild steel, so thread cutting would be limited to softer materials.. Are you aware if this was a production method in the 70's?
They all have a spring washer, I have seen more modern roofing bolts , but always in metric dimensions?

Cheers

Dave

Ray White · Joined: 02 Dec 2014 Posts: 7128 Location: Derby

I believe that is a self tapping bolt for earthing a battery through the lead post.

goneps · Posted: Mon Jan 25, 2016 12:16 am Post subject:

To the best of my knowledge these are primarily intended for use with plastics. I'm pretty sure they were used on the Roland (German) printing machines I worked on around the turn of the 'seventies—probably still have a few lying around somewhere amongst the odd and ends.

Richard

PAUL BEAUMONT · Joined: 27 Nov 2007 Posts: 1281 Location: Barnsley S. Yorks

Dave, I believe that they were, maybe still are designed to screw into captive nuts which have been overpainted. The spiral just creates a reservoir for the removed paint. Rover, or what ever they were called that week, used them extensively for such purposes.

Paul

baconsdozen · Joined: 03 Dec 2007 Posts: 1119 Location: Under the car.

I was told they were designed to fix wings etc and screw into captive nuts where they might be a slight degree of mis alignment. The pointed end means they can be inserted easily and the grooves clear out the thread etc. Probably a cheaper alternative than having the captive nuts in cages where they can move and align themselves.
_________________
Thirty years selling imperial hand tools for old machinery(Now happily retired).

MikeEdwards · Joined: 25 May 2011 Posts: 2710 Location: South Cheshire

I think I'd agree with Paul - from memory I think the seat mounting bolts in my Vauxhall are like this, so they'll be screwing into captive nuts in the floor that have (in theory) got paint and possibly underseal in the threads. Parts list just says "Screw, special".

Peter_L · Posted: Wed Jan 27, 2016 3:08 pm Post subject:

I agree with the use on captive nuts. It would prevent the torque set tools from stopping before the bolt was correctly tightened.

I have found them on my Ford Explorer, body panels (2000-2008) are they still used ?

Did the change to water based paints change things ?

Ashley · Joined: 02 Jan 2008 Posts: 1426 Location: Near Stroud, Glos

FWIW sheet metal workers will put pull ups in thinnish sheet and rather than tap a thread in this hole that a bit longer than the thickness, you buy screws that are case hardened and triangular in section, so cut their own thread on the way through. You see them in washing machines, microwaves and hi Fi boxes and they work pretty well. I've not heard of them in cars but they're not rare.

ukdave2002 · Joined: 23 Nov 2007 Posts: 4240 Location: South Cheshire

My Father in Law (retired Vauxhall Ellesmere Port Plant) confirmed what a number of you had thought; they are used where a item has to be fitted to the vehicle shell after the shell had been painted; bonnets, boots , seats etc, the narrow end is the minor thread dimension, this speeds up alignment, and the spire helps clean out any paint in the captive nut.

Dave

goneps · Posted: Thu Feb 04, 2016 9:58 pm Post subject:

Peter_L · Posted: Thu Feb 04, 2016 10:04 pm Post subject:

goneps wrote:

Ashley wrote:

...you buy screws that are case hardened and triangular in section, so cut their own thread on the way through.

'Trilobular' is the correct term for these.
Richard

and the word for today, children, is "Trilobular". Which now presents me with the problem of how I can introduce my "new" word into a conversation. Smile

Penguin45 · Joined: 28 Jul 2014 Posts: 384 Location: Padiham

goneps · Posted: Fri Feb 05, 2016 2:33 am Post subject:

Dipster · Posted: Fri Feb 05, 2016 9:46 am Post subject:

On a similar subject I spoke to one of my my sons who is a buyer for one of the bigger DIY chains in the UK. I am not sure if his wicked sense of humour is coming in to play here but he told me of a wood screw that is screwed in clockwise for the first third of its length, anti clockwise for the next third, then finished of clockwise.

When I scoffed and questioned the reason for such a complication he said that it somehow affects the grain of the wood in a manner that stops humidity getting to the screw that might cause it to rust.

I have yet to Google this. What do you think? Humour or fact?

MikeEdwards · Joined: 25 May 2011 Posts: 2710 Location: South Cheshire

It'd certainly slow down the "I'll do them all with my power screwdriver, be up in minutes" crowd.

Struggling to see how, once you start on the first change of direction, you're not just chewing up the wood on the first section or, indeed, why the screw just wouldn't come straight back out again.