Hi Ben - All parts that come in contact with food, herbs, etc. are steel. The only aluminum are tubes covering steel side supports, more for decoration - no contact with food. For the money this is an excellent unit for home use.
Hi Ben - Reading the other comments there must be two products on the market. The product I have looks like the image that accompanies this. The only aluminum are side tubes. The strainer and basket are stainless and the turn screw is all steel (checked with magnet) with some plastic caps for looks. The screw will rust - stainless would be too soft, so after each use dry screw and apply a little olive oil. I've done a lot of work with mine.
Not sure, but the plate that presses the fruit is plated with something that has chipped off of mine and the screw has begun to oxidize after just one use. I am currently trying to return mine, unfortunately I'm not having much luck. My advise.... Buy a better product. There was red spray paint all over the screw threads when I took mine out of the box. It took a lot of work to get it cleaned off.
So far as I can tell, every part that touches the food is aluminum. There is a basket-like metal cage attached to the handle which crushes the fruit into the aluminum container, forcing the juice out through the aluminum spout.