Shimano deore piston clean

Hello I remix a STL from PhyMaus, this spacer is for clean and unstuck piston brake shimano VTT, I haven't try yet.
I don't have idea of deep I should need so I take the deep of 2.1mm I don't know is this dimension is safe or not for brake so be carefull.

leave me some comment for upgrade

update: must be updated