Non-standard metric screw thread geometry calculation

Suppose you read on a specification that the mating screw thread of a component is M10,5x0,5. From the prefix M you know that this is a metric screw thread, but you can't find it on a standard metric screw tread catalogue .In this situation you can simply calculate the thread geometry with the below trick. Attention this method calculates the nominal profile for thread mating without clearance on the flank (zero profile).

The calculation start from pitch selection, all metric screw threads have pitch from the below range:

0,2mm  0,25mm  0,3mm  0,35mm  0,4mm  0,45mm  0,5mm  0,6mm  0,7mm  0,75mm  0,8mm  1mm

1,25mm  1,5mm  1,75mm  2mm  2,5mm  3mm  3,5mm  4mm  4,5mm  5mm  5,5mm  6mm  8mm 

Second step is the screw thread nominal diameter. From the figure above and the equations below with known the pitch and the nominal diameter (internal or external) we can calculate all the required dimensions of screw geometry.

 
If we don't want to use the equations and we have a table with standard screw thread dimensions, we can choose a standard size witch has the same pitch and add to its basic dimensions (given in table) the difference between its nominal dimensions with our thread nominal one. Attention on internal and external nominal dimensions, the above  figure will be very helpful.  The table bellow describes the maximum nominal diameter for fine pitch.