There is no generic mesh to use in building a mesh wick...mesh wicks are almost exclusively used in genisis atomizers and though not everything is transferable from using mesh in a genisis to other attys somethings do crossover....and even these things are debateable among genisis users.
different sizes meshes are used for different PG/VG ratios usually the lower sizes are used for heavy VG juices like say #200 or #300 the higher sizes are used for 50/50 juices or higher PG juices #400,#500,#200 super fine.
also there is no generic wick..there are different ways to build a wick that sometime involve using 2 different sizes of mesh or sometimes 2 different wicks within a wick. The direction of the grain is important, some people swear that a mesh wick that is cut diagonally, wicks better...Whichever mesh you do use and however you build your wick,( as long as you build it right and you coil it right) you will be able to get the experince of the flavor that mesh can give,but the ability to build a wick that can wick fast enough and hold enough juice for how you vape,and for the atty design,will take some experimentation, using mesh is notoriously challenging and is why most vapers don't use it, so you need to allow yourself a fair bit of time and failure to learn how to use it.fair warning...a dry hit on a mesh wick makes a dry hit on cotton look like a sweet kiss,be warned..also the boogeyman of most new mesh vapers is getting hotspots out of your build which will absolutely ruin the flavor of your vape and can be pretty nasty tasting. good luck with it,and have patience.if you are a MTL vaper say 25 watts or lower... mesh is something you should master.