Spacers hold nibs in our pens that provide overfeeds. You use a spacer when you don't want to use the overfeed. Just pull out the overfeed and insert the spacer. When you want to use the overfeed, pull out the spacer and insert the overfeed. 

Note: The product photo shows two spacers. You receive one spacer in your order. The photo image is designed to give you a clearer idea of the product.