Had when i worked in a preschool and kids love them! I would use colored sand instead of white salt. DIY salt tray with alphabet cards. Easy to make and kids have fun smoothing out the salt after correctly making the letter
The bolts are graded in diameter for a more difficult exercise. Five slotted bolts and stubby screwdriver. Designed by a Montessori teacher to aid the development of eye-hand coordination and teach a practical skill.