Specification of planetary ball mill often depends on requested capacity for each time. There is a formula for calculating total volume of the 
machines mill jars as following:
Total Volume of Ball Mill (Liters):  A=C/p*3

Remarks:
A indicates total volume of planetary ball mill (unit: L);
C indicates weight of grinding materials (unit:kgs) for one time;
p indicates density of grinding materials (unit:kgs/L)

For Example: 
2 KGS of grinding materials are needed to be grinded at one time,Density of grinding materials: 1.5KGS/LThen, The total volume of planetary ball
mill: A=2/1.5*3=4L.Conclusion: you need to order a set of planetary ball with total volume of 4L. eg. XQM-4 which should be equipped with 4pcs 
of 1L mill jars

All categories of planetary ball mill with total volume of 4L:

      According to functions of the machine, there are four types of planetary ball mill which are called vertical planetary ball mill, horizontal planetary ball mill, full-directional planetary ball mill, and dual planetary ball mill. You have to make right selection of the correspondent type according to requests of material grinding. All models of planetary can be equipped with cooling or warming device if necessary.

     Reference Table For Type Selection of Planetary Ball Mill

Selection of mill balls has to made based on the following factors:
1) Material of mill balls has no impurity to grinding materials;
2) Properties of ball's material such as anti high temperature, wear resistance, and corrosion resistance have to meet request of grinding process;
3) Density and hardness of balls has to be higher than that of grinding materials;
4) You are suggested to make selection as per the following matching table.

Matching Table for Jars & Balls

Tungsten carbide balls and zirconia balls are suitable for tungsten carbide jars

Polyurethane mill jar can be matched with iron core PU balls, agate balls, stainless steel balls, and zirconia balls.

Stainless steel mill jar can be matched with stainless steel balls and steel balls