The red base is a weight sled for strength/endurance training. My steel target holders (the white part) have a central spike that you drive into ground. The spike fit perfectly into the central pipe that goes through the center of the weight plates. A couple bungees to keep the target holder centered. I didn’t have to “make” anything......just stick it together.
Used it today in the STRESS2 class that I ran. Worked like a charm.