The only reason I suggested fine and coarse threads is becaue there's a 0.2mm difference in the recommended tap drill sizes for fine and coarse metric threads
...
If I were so very knowledgeable about threads, I would have answered on that basis. But I am sufficiently with it to try to find an answer. Further, I might well post bollocks on occasion, but most often I have actually tried to look something up, if appropriate.
The Wiki link identifies quite a lot about threads.
thread is smaller than than of a finer pitched bolt of the same o/d. The tapping drill therefore needs to be smaller. The o/d of the thread is however the same.
That's because the tapping drill has to match the core diameter of the thread, and coarse threads have a smaller core diameter than fine threads of the same external size.
Maybe doing "O" level metalwork wasn't such a waste as has been suggested.
By the way, if you want to interchange nuts between thread standards, then the closest is Whitworth and UNC, as they use the same thread pitch for their respective diameters. It's not ideal, though, as the threads are different shapes (Whitworth was normally rolled with rounded tips and bottoms, while UNC was lathe cut with sharp tips and bottoms. The angles are also different.), so the strength of the unit is much reduced. BSF and UNF can't be interchanged and will strip the threads if forced, and BA is in a world of its own...
Fit as in not the way wide legged trousers 'fit' chavs.
0BA and M6 x 1 being a case in point
a metric coarse or fine pitch screw thread is always the same regardless of the nominal diameter.
With regards to ISO metric threads every dimension is derived from the nominal diameter and the pitch. The angle is always the same, 60 degrees.
I thought it was the other way around?
The
Thanks to everyone for all the explanations.
I'd never previously bothered with any of this, but maybe like the OP I bought a couple of digital calipers from Aldi. Using vernier calipers, although good enough for identifying drill bits, there's always a possibility of user error or misreading such as you wouldn't want to swear blind as to any particular reading. Without using a magnifying glass anyway .But now for just £8.50 everybody is an expert. The outside diameter of the thread of the 6mm (Toolstation) bolts I just measured is 5.86 mm. And yes I pressed zero first.
michael adams
...
For shape:-
I may have mis-remembered the manufacturing methods, as I finished the course over 40 years ago...
I suspect that either thread could be produced within tolerances by either method, but the rounded shape would be easier to roll than cut, the squared off shape easier to cut than roll and when made manually, the tap and die are both equally convenient to use.
It would be very unlikely to come across fine and coarse threads in the smaller sizes.
That's within the defined tolerances. The diameter of a bolt is the diameter of the unthreaded portion, which is a close fit in the hole. The threaded portion is specified to be smaller to allow for easier assembly and to allow for manufacturing tolerances. If you were to continue the shape of the thread to a sharp edge, then it would be the same diameter as the shank.
Read this page:-
In fact, the whole site is a mine of information about threaded fasteners.
Looks at two computer screws, both metric, both about 3.5mm, one coarse theaded, one fine. CBA to get out the micrometer to check if they're both metric, but as they both came out of the same case....
The coarse one is very likely an american thread. Most often found for HD fixings.
Nope. One may or may not be metric but one is almost certainly UNC -a US thread used principally to hold disk drives in place.
Hard disk fixing screws are normally UNC, CD/DVD drive fixings are normally metric, so you'd expect to find both in any computer...
Indeed so. But without my £8.50 Aldi digital calipers I would never have thought to measure the diameter of any screw. Metric or otherwise. Similarly I doubt that the OP would have been quite so confident in his measurements in order to ask his question.
I now seem to remember having come unstuck discussing the finer points of screw dimensions on here before.
I have actually read a history of screws and screw threads and their role as an essential element in the evolution of precision tools - Ramsden Maudslay and some French engineer and their original screw cutting lathes - which could then be used to produce lead screws for lathes which could then be used to duplicate the originals
With the real precison laying in arranging the screw threads perpendicular to one another. i.e one compete revolution in one threaded rod only rotating another threaded rod by a 1/60 th of a turn. Which in turn etc. etc.
Without checking ISTR the screw is a form of inclined plane.
michael adams
...
That wasn't what Wikipedia said, but it would make sense.
Then what is your answer?
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.