It is a "double" tamper, approx. 57 mm, on the other side approx. 49 mm (e.g. to press on the conical single strainer half-full for the first time). The 58 Lelit Tamper Rosso with 58.55mm has a diameter that is 1-2 mm larger and is defhinitely more flush with the edge of the 58 sieve than the plastic tamper.