Live centre screw

[J-G]

It looks as if Phil has solved your problem -- the fact that the manufacturers told you 1 - that it was 6 x 1.5 and 2 - that they were available via eBay is most disconcerting!! or that the 'technician' that you spoke to has no idea what he/she is talking about.

I had little in the way of committment this morning so drew up a comparison of the threads in contention. --- incidentally the reference to ¼NPT (@Fergie 307 ) is way off track, That is an American Pipe thread (even forgeting the Taper part) which is 14.67mm dia. ---

This was drawn to show what the problems might be assuming that the existing hole was in fact 6 x 1.5. The green line is what would be left if you re-tapped to ¼BSW and the blue line if done at M7.

M7 taps are available from Tracey Tools who stock probably the widest range of taps & dies of any UK supplier -- no, they do not list 6 x 1.5.

 

[Richard_C]

Hopefully the above suggestions work.

If you can't find the right fit, ask yourself if you really need it. It's convenient, stops the centre falling out when you move things, but in use it's all under compression load anyway so won't go anywhere.

A quick bodge to stop it falling out may be to push a short length of 5mm dowel or similar in the hole and put an elastic band or sticky tape around it. Cheaper than a new live centre. It could have been missing for a while and it remained useable.

 

[Fergie 307]

It looks as if Phil has solved your problem -- the fact that the manufacturers told you 1 - that it was 6 x 1.5 and 2 - that they were available via eBay is most disconcerting!! or that the 'technician' that you spoke to has no idea what he/she is talking about.

I had little in the way of committment this morning so drew up a comparison of the threads in contention. --- incidentally the reference to ¼NPT (@Fergie 307 ) is way off track, That is an American Pipe thread (even forgeting the Taper part) which is 14.67mm dia. ---

View attachment 129238

This was drawn to show what the problems might be assuming that the existing hole was in fact 6 x 1.5. The green line is what would be left if you re-tapped to ¼BSW and the blue line if done at M7.

M7 taps are available from Tracey Tools who stock probably the widest range of taps & dies of any UK supplier -- no, they do not list 6 x 1.5.

My observation was simply that a 1.5mm pitch is just under 17 tpi, and so NPT at 18 was an Imperial PITCH close to that, but did not suggest it as an alternative, as you say it's way too big, and a taper. My point was that 1/4 BSW is not 26tpi as was stated in the reply.
I entirely agree that it doesn't inspire confidence when the manufacturer doesn't seem to be giving good info.
Bit the easiest solution would seem to be to just get a new one from them, after all we don't know for certain that it isn't M6 x 1.5, however unlikely that seems!

 

[Stigmorgan]

My observation was simply that a 1.5mm pitch is just under 17 tpi, and so NPT at 18 was an Imperial PITCH close to that, but did not suggest it as an alternative, as you say it's way too big, and a taper. My point was that 1/4 BSW is not 26tpi as was stated in the reply.
I entirely agree that it doesn't inspire confidence when the manufacturer doesn't seem to be giving good info.
Bit the easiest solution would seem to be to just get a new one from them, after all we don't know for certain that it isn't M6 x 1.5, however unlikely that seems!

Getting a replacement from the manufacturer would be the easiest option if it was an option, I stated earlier that they wouldn't send one out.

 

[Fergie 307]

Getting a replacement from the manufacturer would be the easiest option if it was an option, I stated earlier that they wouldn't send one out.

apologies I must have missed that. Not great customer service. How certain are you that the bolt you tried in the hole is M6, as that does seem by far the most likely option, and would fit with their " we don't supply them because you can buy them anywhere" approach. If you aren't absolutely sure I would be tempted to just go to the local hardware place and buy an M6 bolt. If it fits then just cut it down, slot it, and you're good to go.

 

[Phil Pascoe]

He's already tried a 6mm bolt - I think he would have realised if he were trying a 5mm one.

I'd just drill the other side and tap it 6mm x 1, or maybe 5mm.

 

[Stigmorgan]

The hole is 6mm wide, a 6mm bolt didn't fit. @Phill05 is kindly sending me a couple to try, if they don't work I will try something else but don't want to go down the Macguyver route until I've tried everything else first.

 

[Fergie 307]

He's already tried a 6mm bolt - I think he would have realised if he were trying a 5mm one.

I'd just drill the other side and tap it 6mm x 1, or maybe 5mm.

I was thinking more along the lines that if you have an "imperial" workshop, then you could easily mistake an imperial fine thread for metric, especially if it's amongst a box of bits and bobs. That's why I asked if he was sure the bolt he tried was M6, after all presumably hasn't got a thread gauge or we wouldn't be having the conversation in the first place.

 

[J-G]

That's why I asked if he was sure the bolt he tried was M6, after all presumably hasn't got a thread gauge or we wouldn't be having the conversation in the first place.

Even if @Stigmorgan did have a thread pitch gauge it's unlikely that he could get it in to check the INTERNAL thread at 6mm or ¼" dia. - those gauges are usually used to check external threads - he could posibly take a plasticine cast of the internal thread of course and measure that but it's not easy.

He's already counted the number of thread crests that he can see and adjudged the pitch from the length of the thread which is why he can be confident that it's larger than 1mm but the difference between 1.27mm (20 tpi BSW) and 1.5mm is too close (even at 18%) to determine by eye under the prevailing conditions.

I could certainly separate out a mixed box of ¼"BSW, M6, 2BA, ¼"UNC screws with no difficulty but 'Threads' were my bread & butter for many years - comparing internal threads would be more of a challenge!

Incidentally, your reference to "M6 x 1.5" (in reply #23) is wrong - the 'M' prefix should only be used to indicate the standard coase pitch/dia. combination and 6 x 1.5 is not the standard.

 

[joethedrummer]

,, every day is a school day,, never knew you only use the "M" prefix for standard thread,, thanks J-G

 

[Fergie 307]

I too could tell the difference, that doesn't mean the OP can. Anyway it will be interesting to see what it turns out to be.

 

[Fergie 307]

And I agree that if you simply refer to M6, M8 or whatever then you are referring to the standard coarse pitch, however I think it's a little pedantic to say that M6 x 0.75 for example, is wrong. Many top quality taps and dies are marked in exactly that way, nobody died as far as I know.

 

[Fergie 307]

And in fact the ISO standard says "a metric ISO screw thread is designated by the letter M followed by the value of the nominal diameter D (the maximum thread diameter) and the pitch P, both expressed in millimetres and separated by the multiplication sign, × (e.g., M8×1.25). If the pitch is the normally used "coarse" pitch listed in ISO 261 or ISO 262, it can be omitted (e.g., M8)."
So actually M6 x 1.5 is quite correct terminology, so is M6 x 1.0, although the latter would normally be referred to as simply M6, not at all confusing to the uninitiated !

 

[J-G]

however I think it's a little pedantic to say that M6 x 0.75 for example, is wrong

I'm known for my pedantry

IMO it is wrong - the whole point about any thread designation is that of brevity. You would never describe ½"BSW as ½" x 12 Whit (surely?) - that requires an extra 7 charcters providing just the dia. and the thread series tells anyone all they need to know - if they are not familiar with the 'standard', they can determine all the detail from published information. The use of 'M' before a non-standard dia./pitch combination simply adds a character that imparts potentially false imformation.

I see that you have responded whist I have been typing - - - I am certainly not ' uninitiated' and stand by my opinion even though it may be 'old hat'.

The ISO standard takes account of the fact that there is no 'coarse' and 'fine' designation in the Metric series as there is in the Imperial series. ie. they don't use 'M' and 'm' (for example) - so all non coarse combinations do need more specification.

 

[Fergie 307]

As to measuring internal threads with a pitch gauge, if you have the narrow finger type gauges, or grind down regular ones, it's not too difficult. Admittedly the difference between 1mm and 26 tpi would be a challenge, but the root diameter will give you the answer, and that can be measured accurately enough with a decent caliper, or seeing what size drill will fit snugly in it. With reference to the bolt the OK tried in the hole, how do we know it is an M6? M6 hex bolt will have a 10mm AF head. An imperial 1/4 fine, easily confused unless you really know your threads, will typically have either a 3/8 or 7/16 AF hex head, it will not in any circumstances have a 10mm head.

 

[Fergie 307]

I'm known for my pedantry

IMO it is wrong - the whole point about any thread designation is that of brevity. You would never describe ½"BSW as ½" x 12 Whit (surely?) - that requires an extra 7 charcters providing just the dia. and the thread series tells anyone all they need to know - if they are not familiar with the 'standard', they can determine all the detail from published information. The use of 'M' before a non-standard dia./pitch combination simply adds a character that imparts potentially false imformation.

I see that you have responded whist I have been typing - - - I am certainly not ' uninitiated' and stand by my opinion even though it may be 'old hat'.

My dear chap I wasn't referring to you as uninitiated at all. Merely a perhaps clumsy attempt to keep it light hearted, and illustrate the potential complexity for those who don't share our fascination with fasteners. As I say all my Dormer and other quality taps and dies are marked, for example M14 x 1.0. And the ISO specifies that format. But really who cares as long as we know what we are referring to. Life is too short.
We have come a long way from the original question. My money is on his screw being M6 (x1.0) all along, who would have thought it would have brought about such an interesting discussion.

 

[Fergie 307]

Out of interest are you the same gentleman I had a conversation with about the history of fasteners on Quora some time ago? I think it started around the various ingenious methods used before screw threads became widely used, many of which seem to have originated in woodworking practices.

 

[Phil Pascoe]

I was thinking more along the lines that if you have an "imperial" workshop, then you could easily mistake an imperial fine thread for metric, especially if it's amongst a box of bits and bobs. That's why I asked if he was sure the bolt he tried was M6, after all presumably hasn't got a thread gauge or we wouldn't be having the conversation in the first place.

Fair point. I haven't anything that's not metric, and for 45 years I've only used imperial stuff bought in for a particular job - in my boxes you'd only ever find metric.

 

[J-G]

- I agree that we've 'moved on' somewhat - and yes it's now more about threading in general - and when I awoke this morning I did not expect to be digging into knowledge I gained some 40+ years ago !

As an historical context note - I was for some years head of the Export threading department at Herbert Small Tools, dealing with orders for threading equipment worldwide so being exposed to many 'special' thread forms that most British or American workshops would seldom, if ever, come across.

Ah - No - I don't think I've ever had a discussion on Quora - and I wouldn't have had an opinion about pre "Whitworth" standardisation

You can seldom rely upon the core dia. being the standard root dia. since standard engineering practice is to use a drill to leave something less than full depth to make tapping easier.

As far as measuring the head of an M6 bolt is concerned --- I had assumed he was using a grub screw --- but it could be a Cap Screw, again you would need 'inside knowledge' to determine the 'standard'. I'll bet that you and I could distinguish the difference between a ¼BSF, an M6 and a 0BA grub screw simply by 'feel' and sight but then, we know that the thread forms are quite different.

My previous mention of 2BA (#29) was an error out of context!

 

[Fergie 307]

I use both quite a lot. And my 1993 Jeep is an interesting example of a mixture. Parts that are classiccally Jeep, like the straight six 4litre engine, still use imperial sizes. Many of the ancillary components use metric, so you often end up with a mixture of both while doing a job. So for example the water pump is held to the engine block with 5/16 UNC bolts, but the bolts that hold the two halves of the pump together are M8. All good fun !