Test Cylinders

I am trying to make some pistons, so I wanted to know what size to make the piston. I created the large cylinders and then cut the cores out in incrementing sizes from 0.5mm, 1mm, 2mm, 3mm, 4mm to 5mm. I then reduced these by .9 and printed these. the 0.45mm would not print and the 0.9mm was too small to really do anything. The 4.5mm fits in 5mm,3.6mm fits inside the 4mm, 2.7mm fits in 3mm and 1.8mm fits in 2mm. Each of these fits tighter as the size goes down.