Shale shaker screens have become complicated in the work of the past 40 to 50 years, Initially, they were simple square openings that were simple to explain. At that time, screens were designated by "mesh" openings. The mesh count is the number of openings per inch in directions perpendicular to each other & parallel to the screen wires, For example, a 40-mesh screen would have 40 openings per inch in direction & 40 openings per inch in a perpendicular direction, In a hard work to eliminate calling the screen a "40 by 40" screen, the common terminology resulted in calling the screen a 40-mesh.
A comprehensive document was approved by API and published in December 2004 and approved by ISO in 2006. Two major changes were incorporated into the Recommended Practice:

* Conductance measurement was made more robust
* A new shaker screen description method was instituted.

Most companies were in accord with the first new procedure. Discord arose, however, with the new description method. This arose because most screen manufacturers and solids control service providers now needed to label their screens as coarser than their original designation. Some screens labeled as "XX175" (implying a 175 mesh) would not capture even 100-mesh particles.
Cut points are not a unique property of shale shaker screens. Other parameters also have an impact including:

* Liquid phase viscosity at the shear rate required to move through the screen
* Screen velocity and acceleration
* Deck angle
* Screen motion
* Solids loading and solid sizes presented to the screen
* The gel structure of the drilling fluid, among others.
All screens have some distribution of openings. The Task Group decided to identify the largest solid that would pass through each screen (or the smallest solid captured by the screen); this is called D100. Solids smaller than D100 will pass through a D100 screen. If a screen is labelled as 200-mesh (74 microns), no 100-mesh (150 micron) particles ought to pass through the screen. Clearly all 80-mesh (180 micron) particles ought to not pass through the screen. If openings are 74 microns by 74 microns, larger particles ought to stay on the screen.
The aim was to describe the size of the screen openings. Most particle sieving and sizing is related to some standard opening sizes. Opening sizes, for example, in a 200x200 mesh screen will depend on wire thickness ASTM Specification E-11 serves as an accepted standard to describe screen openings. The Task Group desired to generate a standard method of describing screen openings that would be reproducible around the globe and would be comparatively simple.