Shabbos 25:2

Some utensils have purposes that are prohibited on Shabbos. These include things like a grinder and a mill, because we are not permitted to crush or grind on Shabbos.

Shabbos 25:3

Any utensil whose purpose is permitted may be carried on Shabbos regardless of the utensil's material. These utensils may be handled both for the sake of the thing itself and in order to use the place that it occupies, as well as to use the item for some purpose. Utensils whose purposes are prohibited may be moved if one needs the place that it occupies, or to use it the object for a permitted purpose but not for the sake of the item itself.