My final design consisted of four components.
A cap which can be used to assist the user in gripping smaller fruits like limes and lemons.
A reamer with ridges that tear into the fruit, extracting both juice and pulp. The holes are sized to filter seeds but allow pulp to pass through.
A base which is shaped to be held by any hand size, and which funnels juice into any container.
A removable silicone plug which allows the juice to be stored without leaking.