M10 x 1.5 ?
That's a fairly typical thread designation that you might see, but
what do the letters and numbers actually mean?
Let's start with the M10 part. The big M means that this is a metric thread. The 10 is the nominal outside diameter of the thread. In tech speak the major diameter. In this case it would be 10mm.
The picture shows the major diameter of a thread being measured. You can see that it is actually a little bit under 10mm. It is usual for the actual outside diameter of a thread to be slightly smaller than its designated value.
1.5 is the thread pitch
- the distance between one pointy bit of a thread and the next one along, in this case 1.5mm.
Not a great picture (below) but these are both M10 threads. The top one is 1.5 which is a fairly standard M10 thread pitch. The bottom is 1.25. You should be able to see the difference between the two.
The braking system on motorcycles is often an area where finer thread pitches are used. So if a bolt doesn’t fit, check carefully that you’re using the right pitch bolt.
One final useful thing to know is the internal diameter of a thread (Minor dia.) For M10 x 1.50 this is around 8.50mm. This diameter determines the size of tapping drill used.
