These are Carabiner clips from Cimarron Sports (also called D-Clips) - used to attach your batting cage net to your frame or frame cables.

Features:

• Come in a pack of 50 or 100
• Spring Snap Link - 3/16 in. size zinc plated
• Each 50 pack weighs about 5 lbs
• Measure 2 3/4" long
• We recommend using 1 carabiner every few feet (connect to the roped border of your net)
• Use the clips to slide your batting cage net along cables like a curtain
• You can also add rope or strings to them and use them to connect to a stationary batting cage frame