One of the toys bought for my daughter that never really excited her imagination was a set of wood screws and threaded disks that my sister sent for a birthday. They are lovely Plan toys which always are great quality and are also very environmentally friendly. Regardless of this, my daughter only casually played with them.
My son, however, is fascinated by them and will sit for long periods of time screwing and unscrewing the pieces. It seems he is very ready for this right now.