White push-on 3/4 inch pipe clamps to attach Greenhouse Film to Hoops and purlins. These are made of ABS so they don't have the Chloride that deteriorates the UV protection of 4 year Plastic.  Inside Diameter (ID) of ABS clamp is 0.90 inch; The allowed range is 1.046 - 1.054 in Inches.  If your hoops are made of PVC, keep the 4 year plastic from touching the PVC with a thin layer of tape and clamp over the outside with these clamps.  Spacing recommendations of 2-4' depending on the windiness of your location.