The small round piece is too big in diameter to hold the pen... The pen just falls out!
If the product is not shipped. The clip that needs to go around and hold the pen is too large in diameter and just slides around the pen, allowing the pen to fall out when you use it. Do not buy this product defective and may cause injury or death!
Pros
Protection: Excellent anti-fall pen with anti-fall buckle, can be locked tightly.