has locating features 260 cut into its bottom that mate with interlocking features also referred to as locating fingers 270 see fig1 on the bottom plate 20 of the milling vessel 10 top plate 30 of the milling vessel 10 also has locating interlocking features also referred to as locating features 280 that mate with the locating fingers 270 of an adjacent bottom plate 20 when vessels 10 are stacked as the milling vessels 10 are stacked in the holder 190 the mating locating features 280 and the locating fingers 270 interlock to prevent the stack from rotating and lock it in place once the milling vessels 10 are assembled into the holder 190 the motor assembly 210 is moved into the engaged or run position as shown in fig7 referring to fig6 the motor 220 has a motor adapter 290 rigidly attached to its front face 300 the motor adapter 290 has locating features 310 similar to locating fingers 270 locating features 310 engage in the locating features 280 of the top plates 30 of the milling vessels 10 the locating features 310 will engage with the top plate 30 of the milling vessel 10 that is on the top of the stack in the holder 190 once the motor assembly 210 is locked in the run position the motor adapter 290 holder 190 and the stack of milling vessels 10 are all locked together and cannot move fig8 shows a cross sectional view of this state fig9 shows a cross sectional view of a portion of the motor assembly 210 engaged with the top milling vessel 10 of the stack the motor 220 has a drive shaft 315 with a motor magnet carrier member 320 rigidly attached.