Can anyone explain to me what the difference is between an M12 x 1.25 and a M12 x 1.75, M10 x 1.5 and a M10 x 1 Tap and Die please ? And when you why would use one as opposed to the other of the same size
Not a problem but you need both.
Lets take the M12 ones.
The diameter of the bolt is 12mm the distance between the threads (or pitch )is either 1.25mm or 1.75 mm depending which one you chose.
Now this is where it gets a bit complicated Mazda tend to use the coarse threads in most places therefore M12X1.75 and M10x1 but you will find that bought in components like suspension and brakes parts may use the finer threads.
Further it is not unusual and I had it on Subaru rear struts that different replacement struts had new nuts supplied that were different diameter and and pitch on the threads.
Suzuki tend to use coarse threads but the track rod ends on the Jimny Jeep are fine threads.
I keep a good selection of nuts and bolts in my garage so that I am not caught out when working on cars when a nut or bolts falls somewhere you cannot find it.
I also now keep fine threaded nuts and bolts in M8, M10 and M12 and in certain cases there are both fine and super fine and in those cases, I have a selection of both fine and super fine nuts and bolts.
Clear as mud I hope and you also need a thread gauge to allow you to measure the thread pitch on a nut or bolt that does not want to screw together.
Forcing components to screw together in is very bad practice.
I probably have at a guess 30 different small drawers of different size nuts and bolts and friends who use my garage marvel at my selection of nuts and bolts but in reality just £20 spent on making car spannering easier.
It is usually only proper garages that have stock of different nuts and bolts.
Fine threads tend to be better at not loosening when subject to vibration like suspension, the aircraft industry uses fine threads for that reason.
https://en.wikipedia.org/wiki/ISO_metric_screw_thread
I would add that tap and die sets are used to make the nuts and bolts or rather to cut the pitches.
The tap is like a bolt with a taper in at the front to allow it to start to key before it cuts the thread in the nut or equivalent receiver.
The die is the piece that has the appearance of an elaborate nut and as an example is wound onto 12mm bar to make M12 bolts - it simply carves threads into the bar. Again it tapers but this time out to ease its way onto the bar to key.
Taps and dies can be used to check thread gauge and pitch in their opposites ie tap to nut and die to bolt.
If you have a full set covering all the bases most sets are short of most fine ones.
Really to answer the question it depends on what the application is.
M12 x 1.75 and M10 x 1.5 are metric coarse, the standard ISO thread.
M12 x 1.25 and M10 x 1.25 are metric fine threads.
M10 x 1.0 is extra fine thread.
Usually the coarser threads are used on softer metals.
Usually on Japanese cars (and motorcycles) they use the standard or coarse metric threads up to M8 x 1.25 then use either metric fine or extra fine.
This explains it a bit.
https://en.wikipedia.org/wiki/ISO_metric_screw_thread