Lotus Elan

Bolt Thread Patterns and Sources

PostPost by: Certified Lotus » Wed Jun 10, 2015 9:39 am

I think a full threaded bolt is called a hex head tap bolt in the U.S.

With regard to the packaged bolt kit mentioned, there are going to be a number of issues. First there are no lock nuts included. All suspension and drive train nuts should be using lock nuts (and remember, only flat washers with lock nuts, not lock washers). The use of tap bolts is not a good idea where you are going through sleeved parts. There are sizes in the kit mentioned you do not need. And other sizes you do that aren't included.

As I am in the midst of a full chassis, drive train and suspension rebuild on my S1 I made the decision to only use grade 8 bolts, nuts and washers.

You would be much better off to to use the bolt list mentioned, cross reference with an on-line bolt supplier and order what you need. I ended up spending about $150 to replace everything in grade 8.
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PostPost by: RichardHawkins » Wed Jun 10, 2015 11:05 am


Bolts and nuts or threaded fasteners can be a bit of a minefield. Some systems are so similar that you can get the wrong components to go together. Some will work such as UNC & BSW and will probably be serviceable whilst others can be dangerous.

Our Lotuses were made at a time when the British motor industry had adopted the American Unified Sytem (UNF & UNC) fine and corse threads. As others have said, the bulk of the fasteners on our cars are of these two systems, but there are a few BA (British Association) and BSP ( British Standard Pipe).

I suggest you buy some reference charts, usually pocket size, and thread gauges. Thread gauges come in a small pack, a bit like feeler gauges or a multi bladed pocket knife. When you open the thread gauge pack the gauges look rather like short saw blades, and each one has the thread pitch or threads per inch marked on it. Take the bolt you need to identify and work your way through the thread gauges until you find one that fits. Measure the diameter of the bolt. With the pitch or threads per Inch, and the diameter known, you can use the reference charts to identify the bolt.

Years ago I also had a box of odd threaded fasteners, and eventually got fed up with tipping them all out and rummaging through them. I sorted them by thread type and diameter and keep separate thead type and diameters in small cardboard boxes.

I think it is impractcal to keep your own stock of everything you need, when you also consider the different lengths and strengths of steel you will need. As someone else advised a fastener stockist is probably better suited to your needs especially as the bulk of fasteners are from American Standards.

I cannot advise where to get thread gauges and charts from in the USA, but I think there is a national hardware chain called McMaster Car.

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PostPost by: Craven » Wed Jun 10, 2015 1:17 pm

It helps if you can gain some understanding of the detailed function of fasteners being replaced. Its size, grade and thread profile will have been determined in the design stage and many bolts for instance, will have been made specially to meet this requirement. On our cars there are very few over the counter fasteners that meet the original specifications, beware.
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PostPost by: Bud English » Wed Jun 10, 2015 2:02 pm

Great primer on US threaded fastener terms here: http://www.mcmaster.com/#standard-cap-screws/=xkaioh and here http://www.mcmaster.com/#about-screw-an ... es/=xka4by. If the link doesn't take you directly to "About Screw and Bolt Differences", click on that phrase in the far left column.
It's really a topic too big for a quick answer on the forum. :D

Added: These guys will be able to help and have a local branch near you. https://www.fastenal.com/locations/details/SCCO1. We actually have a branch located in our little town due to the mining here. Sometimes pricy but good quality general fasteners.

Edit: I'll also add a caution here not to be tempted to switch to stainless fasteners in areas where fastener strength is a factor without doing your homework. SS is great though for trim fasteners and the like to combat rust.

...and I'll quit editing this now. :wink:
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PostPost by: Gray » Wed Jun 10, 2015 4:56 pm

From memory, a bolt should have an unthreaded section, a set screw is fully threaded, but is often referred to as a bolt.
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PostPost by: jbeach » Wed Jun 10, 2015 6:39 pm

Thank you all. This has been amazingly informative. Learning the subject is complicated has also made me feel a little less ignorant for needing to ask.

I'll have to admit the most wonderful info is that we actually have a "bolt store" here in Columbia SC. I'm headed to the Fastenal store on Saturday!

I believe I'll hold off on the assortment purchase until after I've visited Fastenal with the Lotus-specific list.

Thanks everyone. This forum is amazing!

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PostPost by: pharriso » Wed Jun 10, 2015 9:04 pm

& if all else fails https://www.nutty.com/
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PostPost by: nomad » Tue Jul 28, 2015 2:03 pm

Wanted to add that any decent farm supply store's will have a large selection of bolt's and nut's as well. Also remember that grade 8 bolts are bridle compared to grade 5 and may not be suitable in every application.

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PostPost by: jk952 » Thu Sep 03, 2015 8:52 pm

And in answer to a question than mabe just I wondered,
"what is the std. bolt shank length to thread length relationship?";
here is another boltdepot link:

https://www.boltdepot.com/fastener-info ... ength.aspx.

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PostPost by: bill308 » Thu Sep 03, 2015 10:15 pm

These folks may also be helpful.

http://www.aircraftspruce.com/catalog/s ... nbolts.php

It seems AN bolts are available in a variety of materials. The way I read it, they must meet a tensile strength of 125 ksi. I believe this includes ss ones. This is a very good steel specification. Anybody know the specs on grade 5 bolts?

The beauty of AN fasteners is they give you a very good material and some choice in length and grip length.

AN-bolts may be available in 18-8 and 316 ss.

I plan to use ss bolts on my 26r street car wherever it makes sense. In the north east USA there may be exposure to salt and I really don't want to deal with rust any more than necessary.

I would like to use ss bolts for all body and suspension applications. Anywhere rust/corrosion may be an issue.

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