This is a great (Engino Mechanical Series – Cams and Cranks) product and I was very surprised at all that came with it!  My 7 yo. son likes to take things apart, fix them and then put them back together.  So this is super perfect for him!  The pieces snap easily and stay together.  He was able to follow the directions on his own with minimal assistance. The companion booklet is very thick with detailed “take it further” and exploring different cranks (remember the early model T?!).  I am looking forward to using all the other sets and really digging in with him once fall arrives.  I can see this lasting for a long time and getting a lot of uses.  One thing is the string, it is super long and can be difficult for him (and me!) to manipulate in place.  The directions are not clear on whether it should be cut or what…But that has not spoiled the family’s enthusiasm on this product.  :) Highly recommend it.