A hypothesis is an educated guess or proposed explanation Some research or limited evidence is usually taken into account prior to the development of a hypothesis.
In order to make a reasonable hypothesis for your given situation, the term “density” needs to be understood. Density is defined as the mass within a given volume of a substance. Thus, grams per cubic centimeter is the preferred unit used for the density of a substance.
Therefore, if the screws are of equal size, I would propose within my hypothesis that the screw that is the heaviest to the touch has the highest density.
The actual density of the screws can be found using water displacement and a balance. Penn State provides directions to a similar lab that may be helpful.
I hope this helps!