Which o-ring do you need?

The Pietro uses three seals, and they are easy to mix up because they look alike. The lid o-ring (Fiorenzato 200000344) sits between the hopper lid and the burr carrier. It is the one to replace when the lid stops seating properly, feels loose, or lets coffee dust escape while you grind. The inner grind chamber o-ring (Fiorenzato 200000343) seals the inside of the grind chamber, keeping grounds contained and the chamber seated as it should be. The removable flange o-ring sits on the grinder’s removable flange. It has no Fiorenzato part number of its own, so we stock a standard metric ring in the matching size.

If you are not sure which one you are holding, measure it. The lid and grind chamber rings are both 2.62 mm thick and differ in diameter: 56.82 mm for the lid ring and 66.35 mm for the grind chamber ring. The removable flange ring is clearly thinner at 1.5 mm, with a 58 mm inner diameter. Its diameter is close to the lid ring’s, so thickness is the quickest way to tell those two apart.

Why seals wear out

An o-ring is a wear part. Coffee oils, repeated disassembly and ordinary ageing harden the rubber over time, and once it hardens it no longer compresses enough to seal. The usual signs are a lid that rattles or sits proud, grounds escaping while grinding, and a container that no longer feels airtight. Swapping the ring takes under a minute: lift the old one out of its groove and press the new one in. No tools, no adhesive.

If the grinder is apart anyway, it is a sensible moment to look at the burrs. The Pietro replacement burr set is sold separately in both B-Modal and M-Modal geometries, and the Pietro grinder add-on pack covers the dosing cup, funnel and brush if any of those have gone missing.

Cleaning without shortening seal life

Fiorenzato’s instructions for the Pietro are dry cleaning only: no water, no chemicals and no abrasives, just a dry cloth and a stiff brush on the burrs and the chamber surfaces. That advice matters as much for the seals as for the burrs, since detergent and hot water speed up the hardening that makes an o-ring fail in the first place.

Specifications

The grinder these belong to

New to the Pietro, or looking at one? This review covers the grinder these seals are made for.