For use as a combination sorting and manipulative exercise, this set includes three bolts in graded sizes: 3" by 3/8" diameter, 2" by 5/16", and 1" by ¼". Each bolt is fitted with a washer, a hex nut, a lock washer, and a wing nut.
If children start with assembled sets, they can take them apart and sort them either by item (all bolts together, washers together, etc.) or by sizes (all the parts of one set together), and then reconstruct them. Ages 3 to 6.