Whitworth v UNC

It is useful to note that the Unified standard has five tolerance classes

Which helps explain how there comes to be a range of perceived ‘compatibility’ with Whitworth threads.

MichaelG.

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More authoritative references are available, but Wikipedia should suffice: **LINK**

https://en.wikipedia.org/wiki/Unified_Thread_Standard#Tolerance_classes

That's encouraging. Thank you

I have written to the Seller and asked for clarification as to whether it's BSW or UNC on the blocks listed.

MC

It came from the AAIB report. Thanks to peak4 for posting the link.

I check my facts before posting. It would behove you to do the same before casting aspersions.

Andrew

What a good question! I can't remember ever using the threaded holes in my blocks, which I bought expecting them to be metric. I just checked - they're; M8, which doesn't help MC at all.

My guess is MC's blocks are most likely 3/8"x16UNC because it's a current thread-form common in the US. BSW is unlikely because it's been fading away since the UK standardised on Unified Threads in 1948,. BSW survived in UK motor manufacturing until about 1980, but since then hasn't been used in new designs. Unified threads didn't replace BSW wholesale in the UK because metrication provided a better alternative.

BSW and UNC ⅜ x 16tpi threads fit together, but it's not recommended. The fit is weak because the thread angles are 5° different - low holding strength, and liable to come apart when vibrated. More likely to be done by accident than deliberately but the bodge may not matter in 1-2-3 blocks. If it does matter, the Internet is your friend. Although new BSW are hard to source, there are loads of people selling them second-hand on ebay. UNC are available new, but they too are gradually fading away.

Advice to anyone setting up a new workshop in 2020, go metric young man!

Dave

If you search for 25 50 75 blocks you will find them with 3/8"x16 threaded holes, clearly 123 blocks that have been ground just a little bit more. So if you are making a single base part that is then finished to suit different markets a UNC thread would make sense as the USA would not want a Whitworth thread form.

Martin C

Who watches the watchers ??

Hi ,What new vehicles were still using Whitworth in 1980 ?

There are plenty of new BSW nuts and bolts of all types on ebay ,probably hard to get in diy store.

Maurice

The other thing to watch is a lot of 123 blocks are not drilled clearance size for whatever thread is used in the other holes so if you intend to bolt them together at some time get ones that have suitable clearance holes such as the metric ones from ARC. I don't screw them together often but it can be a useful feature some times.

Also be very cautious about 25x50x75 blocks if searching the net, these for example could be one of 3 different sizes and good luck to your tap if you want to thread the "hardened" steel 

Edited By JasonB on 18/11/2020 10:16:57

Hi, JasonB is correct, the unthreaded holes in my blocks are 5/16", but there are only 5 holes centrally placed as you would find the five dots on dice and they are only through the 1" thickness. You can of course use threaded rods or long bolts to hold two together, but you would have to use 1/4" or 6mm for alinement purposes and you would of course have bolt heads and nuts sticking out, but in my opinion 1-2-3 blocks don't really have much or little use bolted together, unlike the ones that Arc sell, as they were designed for bolting together.

Regards Nick.

I've now looked at the Arc catalogue and can't see which of the holes are threaded.

Can anybody tell me this please?

I'll strongly consider the Arc blocks - but the Carriage adds a substantial on cost.

MC

Re the BSW / UNC holes.
It may depend upon the origin country of the blocks.

Some of the kit made in India seems to be BSW, I guess from colonial legacy. ( That seems to be true of the older kit I've seen, not sure if it's still the case these days)

Taiwan and China seem to be metric unless an imperial thread is specified, which then seems to be Unified.
I'm guessing that is imperial measurements are specified, this is most likely for the US market, and hence the choice of thread.

Bill

Very many thanks for taking the time to photograph the block and post it.

In my view, that's an odd combination.

With best wishes and thanks again.

MC

Further to andrews informed comments, there were other aspects to this.

1/ The "fitter" was actually a manager, who while technically qualified (a licenced engineer), no longer reguarly worked "hands-on" He was doing the work because of staff shortage due to industrial action.

2/ The screws went into thin-wall anchor nuts that are deformed to provide self locking. This ment the 8-23 was tight.

3/ The engineer used the prescribed click type torque wrench but did not have a magnetic holder for the 1/4" hex drive screwdriver bit. He used a standard 1/4" socket and held in in lace by hand. Access is awkward and it is thought he mistook the click of the 8-23 skipping threads in the deforned nut for the click of the torque wrench. He could not see the screw turning because his hand holding the bit was in the way.

4/ Windscreen fasteners are not critical items so no dupliicate inspection is required.

5/ it is thought the 8-32 screws were in the wrong bin.

Not part of the report but personally I think the pilot was probably leaning forward, possibly investigating noise from leaking air, when the windscreen panel blew out. If he had been sat back with harness fastned it is unlikely that he would have been sucked out. It is also rumoured that the crew who saved him by holding his legs thought he was fatally injured and were more concerned about his body hitting the tail of the BAC 1-11 and causing loss of control.

As usual with accidents this did not have a single cause but a chain of events.

A more recent fastener error which fortunatly only resulted in extensive damage to the aircraft (Ryanair 737-800) shows he systen is not infallible. This critical nut with dual locking was left off completly when Boing built the aircraft resulting in parto f the under-carriage coming through the wing.

http://www.aaiu.ie/sites/default/files/report-attachments/Report%202020-014.pdf

Robert G8RPI.

Edited By Robert Atkinson 2 on 18/11/2020 13:13:11

The vehicles to which I referred were 1960s vintage, at the time when Leyland changed from Whit to Unified.

Consequently things like brake slack adjusters soon became mixed, since the the only difference was the hexagon on the adjusting bolt!

The problems came whern they introduced the 500 Series engine with Metric threads, so you had a metric engine in a supposedly Unified chassis, which still used parts from the Whitworth form era! A fitter's nightmare, needing three sets of spanners.

Unified nuts were always identified with multiple circles and I think that in addition to the bolt heads being forged with "UNF" or "UNC" there was a small nick on the edge of corner.

Unless Rolls Royce Oil Engine Division was unusual in the late 50s and into the mid 60s?

Eventually the practice died out, by the 70s. When Perkins began changing from Unified to Metric, the colour of the plating was different, and the Metric hardware was washer faced. So even if no one could spot the difference in thread pitch there were physical differences, as well as colour difference.

If the blocks are 1, 2, 3 I would expect the thread to be Unified, if 25, 50, 75 and Metric, I would expect Metric threads.

Who expects wants to buy 2 meters of 3" x 2"? I know it happens, 6 feet of 25 x 50!

Howard

Hi MC, yes you might think it's an odd combination, but it is surprising how versatile the combination actually is. Below are photos of a set-up I did some while ago, using six 10-20-40, two 20-40-80 and two 1-2-3 blocks and it was all built up before setting into position on my mini mill.

If you look between the two hold down bars, you should see there are four bolts, two from each direction, nipping the two bronze castings between two of the 10-20-40 blocks.

Regards Nick.

P.S. you can actually only see three bolt heads, one on the left as the other is hiding behind one of the other small blocks.

P.P.S. corrected my 30 mistake to 40 after reading JasonB's post. 

Edited By Nicholas Farr on 18/11/2020 14:01:06

Here is what the late JS had to say about them, I've not altered the text as the PC thing was not his way, thread was titled 10-20-40 blocks.

Plus 20-40-80's

Come on lads get your hard earned coin out and get splashing.

**LINK**

Top of the page.

Bit of history first, the original 1-2-3 blacks were made by Starrett and the idea was they bolted together to form angle, tee's, used as packing or to bolt items to to preserve squareness.

One of those items that never had a specific designed use but was different thing to different people, very useful.

However at some stage these blocks went over to Taiwan and were copied but they drilled all the holes tapping size for 3/8" UNC, tapped some then hardened and ground them before changing the un-tapped holes to clearance holes.
Result is they wont bolt together as designed and since then millions of sets have been copied and made in India, and China. Even the Starrett ones are now wrong as they have them made out.

Another problem even for people with decent sized machines is they are too large, at 1" high they are 2" wide and at 1" wide they are usually taller than the average vise.

Soooooooooo, may I present these blocks above?

Again hardened and ground but they CAN bolt together and are of a size to suit most muddle enjuneers.

Listed as The Stevenson blocks because that cretin Ketan at ARC is still pissed off I gave him a quid for a nearly new X3 CNC mill and I told him not to name them after me. Wouldn't have been bad if I got royalties but the tight bastard wants the mill back first and not prepared to give me the quid back.

Seriously nice bit of kit and my pre production set has been in use daily for the last couple of months, in fact the 1-2-3's haven't been out the drawer.

Full marks to Ketan for listening and getting something done about them.

John S.

"Hi ,What new vehicles were still using Whitworth in 1980 ?" asks Maurice Taylor.

I was employed by Hampshire Fire & Rescue as a vehicle fitter in the 1990's and one of the vehicles in the fleet was a new Water Carrier mounted on a Leyland 2-axle chassis. Can't remember the model type or its registration mark after all these years, but I distinctly remember that many of the threaded fasteners on the engine were Whitworth thread form. Not a problem really, as we had several Series III Land Rovers in the fleet and they were Whit. also. Trouble only came along when we had a new stores manager, and he in a fit of enthusiasm decided to tidy up the stores and despatched all the Whit/BSF fasteners to the skip.Replacements were very difficult to source.

This thread has drifted into the topic of 1-2-3 blocks ... so may I refer readers back to: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=57490&p=3

My preference for the smaller heads of Imperial hexagon-socket screws remains.

MichaelG.

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The 1 is, I believe, an indicator of its tolerance class

MichaelG.