The plastic bag of these rings was already opened when I received it. Also, none of the rings were marked with their respective thickness on them, which is disappointing, because I now have to take note of their thickness myself and have to keep the rings separately from each other. Additionally, here are precise measurements I took with a micrometer of all the rings in millimeters: 0.53 (should have been 0.5) 0.51 (should have been 0.5) 0.495 (should have been 0.5) 0.48 (should have been 0.5) 0.28 (should have been 0.3) 0.19 (should have been 0.2) 0.18 (should have been 0.15) 0.10 (should have been 0.1 - the only perfect ring) I guess they will get the job done, but for this price I expected a higher precision. 0.15 and 0.2 mm rings are practically indistinguishable, and all of the 0.5mm rings were different with an amplitude of 0.05mm, which is quite large having in mind that this is exactly the difference the manufacturer offered originally between their 0.1, 0.15 and 0.2mm units (meaning they are incapable of producing precise rings).