A flat base describes the shape of the working face. A spring describes how the mechanism responds as the user presses. A self-leveling collar guides alignment at the basket rim. A single tamper can combine all three features.
Decide how the tamper should feel
For a fixed design, start with the desired grip and overall height. If your design includes a spring, explain what the user should feel during the press and identify any target force or travel you want assessed on a sample.
Review how the collar meets the basket
For a self-leveling design, share the target basket or rim dimensions and show where the collar should sit. During sample review, check that the collar seats as intended, that the base moves freely and that the assembly can be cleaned as planned.