Enablemart.com contains two different types of pencil-grips. Price ranges from $5.45 - $21.75
Thewritingpenstore.com contains verity of pencil-grips rangeing from $1.79 - $5.95. They also includes the type of pencil-grips that are sold in Enablemart.com.
The grips at Enablemart are created by occupational Therapist. It helps the students to hold the pencil with the fingers in the proper position.
The grip prevents students from immature grasping habits. It can be used by right- and left-hand and it has a tripod grasp making it easier for the user.
https://www.youtube.com/watch?v=3pSGEg0eJrw