Thread identification

[Blanco]

Just getting to grips with the new toy, an old 2 door Range Rover from 1980. Just having a hoover out and stripped out the carpets to dry it out.  I realised the rear seat brackets have been removed and only put back with a single bolt (instead of the usual 4) each side. It is one of many disappointments with this vehicle!  As the nuts are captive in the side frame the bolts must be the correct ones. I am no expert on thread forms although I know that Land Rover use most of them over the years so I was looking at thread pitch gauges that are available and whilst I can find metric and Whitworth in abundance, the likely candidates of UNF and BSF seem much harder to find and there is little or no detail on the thread range covered. Does anyone know what these bolts are and or have any tips for good gauges to look out for please?

[TSD]

There's lots of articles around the web on the correct way to identify fastener threads. If I think it's one of the usual suspects, and I have a sample bolt, then my usual method is :-

Measure the o/d of the thread as well as possible - might be vernier, ruler or mk1 eyeball depending on circumstance.

Rub the thread on a piece of white paper, leaving a nice flat mark of the thread pitch, thats easy to measure with a ruler.

Armed with major thread diameter and threads-per-inch, consult these pages :-

http://mdmetric.com/tech/tic1c.htm

http://mdmetric.com/tech/tic1d.htm

That will usually give you the thread ID straight off, without getting into thread forms etc., or at least give you a couple of likely candidates to consider.

If you can find the bolt LR part number, that will usually decode to identify the thread. Look here for guidance.

[FridgeFreezer]

These things are also quite handy around the shed:

https://www.axminster.co.uk/axminster-4-piece-universal-thread-gauge-set-102551

https://www.axminster.co.uk/metric-imperial-thread-pitch-gauge-900472

Although a vernier spanner gets you most of the way.

[Peaklander]

A cheeky non technical method, if you can find the LR part number from the book, is to type it into the search field at www.lrseries.com. Their site part references are very detailed and almost always give the thread and length. If you feel guilty you can always bob an order into them for something.

[Blanco]

This forum is just the best,....... I spent a lot of yesterday on this on and off (when you start going round and round in circles on the net it gets frustrating).

Straight away though TSD comes up with that LR part number scheme, which is great. FF neatly summarizes where I got to, (perhaps I should have waited!) I learned that the major diameter is key and ordered some tables; and Peaklander throws in the tip about LR Series. which means I am now much more confident about the whole subject. ... Result.

In case anyone has the same difficulty I am pretty sure they are 1/4" BSF x 5/8" long , I am off to check out the availability, thanks all.

[lo-fi]

http://www.namrick.co.uk stock a great range and are excellent for less common sizes. 

[David Sparkes]

My starting point is that I don't think Land Rover would have used BSF form bolts or screws in a 1980 anything. Britain had been moving to the Metric system well before then, so 'metric' would be my first choice, with the previous standard, UNF, being my second choice.

I no longer have access to a parts number database for Range Rovers, even for older ones from 1980. If I had, I'd look to identify the bolts used for the rear seat brackets where the nuts are captive in the side frame. As only one instead of four bolts per bracket have been used I think you are on a hiding to nothing try to use one of those two bolts as a size guide. It's highly likely that the installer used what came nearest to fitting, not the correct item.

What you can probably take from it is a close approximation to the major diameter. Whatever you measure, my tendancy would be to round it up to the nearest mm, then look for a bolt / screw in that size and try it in the captive nuts that WERE NOT used by your two bolts.

If you post a request in the Part Numbers section of the forum, someone who still has access to a parts list may well give you the number, which you can run through TSD's handy break back guide.

Regards.

[Ex Member]

5 hours ago, David Sparkes said:

My starting point is that I don't think Land Rover would have used BSF form bolts or screws in a 1980 anything. Britain had been moving to the Metric system well before then, so 'metric' would be my first choice, with the previous standard, UNF, being my second choice.

Almost all fine thread bolts on Series 3s, 90s, 110s, Defenders are UNF, not metric.  If it is fine thread, it is most likely UNF.

[David Sparkes]

14 minutes ago, Red90 said:

Almost all fine thread bolts on Series 3s, 90s, 110s, Defenders are UNF, not metric.  If it is fine thread, it is most likely UNF.

Yes but ... If someome has assessed a thread as BSF, I think it more likely that a BSF 'might' be forced into a metric thread, but unlikely that the BSF form be forced into a UNF thread.

That's why I made Metric my first choice, but none of us can really judge just how brutal an unknown 'mechanic' might be, so I think we will be much more certain if Western et al can produce a part number.

Regards.

[Ex Member]

Actually, it is more like that BSF and UNF can be mismatched.  They are the same diameters and many pitches are close or the same.  There will be no metric fine thread bolts on a 1980 RR.  You are simply confusing the situation.

It is simple enough for anyone to look up the part numbers.  No idea why you want Western to do it.

[Ex Member]

Had a look.  Yes, all 5/16" UNF.  Anybody working on LRs should have a stock of 1/4" to 3/8" UNF fasteners as they are super common.

[Bowie69]

Even my '91 RRC is imperial on the body, and indeed the engine.

[AV8R]

I worked on a 2006 110 last year and I expected it to be metric. The seat belt bolts looked like they would be M11x1.25 . . . . . . Turned out to be 7/16"-20 UNF !

[Ex Member]

5 hours ago, AV8R said:

I worked on a 2006 110 last year and I expected it to be metric. The seat belt bolts looked like they would be M11x1.25 . . . . . . Turned out to be 7/16"-20 UNF !

All seat belt bolts in all cars are 7/16" UNF.  It is an industry standard.

[Blanco]

Curiouser and curiouser.......... the parts book I ordered turned up yesterday and they are indeed listed as UNF but counting threads on the bolt I have I get just under 26 TPI (I only have 5/8ths to work with, and the screw pitch gauge hasn't arrived yet), UNF should be 28TPI. I have ordered both now so I have to see which one suits, ... and then  I will have known comparisons  to hand so it should help  the next time, I don't want to be ordering 2 or 3 of everything!

I think 1/4 is probably the trickiest? hopefully other sizes won't be so bad.

 

[Blanco]

Sorted now, it was UNF, I need to re-dress the points of my vernier caliper I think. The screw pitch gauge turned up and so did the UNF bolts.  (BSF were ordered first but still haven't arrived. )