CollarSafe 1" Wide Designer Patterned Polyester Replacement Collar - ONLY Fits Invisible Fence Models R21, R22 & R51 (1-5/8" Apart on Center) Patterned Polyester Material - CollarSafe's Strongest Replacement Collar Width: 1 inch - Length: adusts up to 30" neck (EASILY customizable shorter by customer-see included instructions) - Thickness: approx .078" or 2.02mm - Tensile Strength: 5,300 lbs (Note: these may be too thick/heavy for smaller petite dogs) These are NOT traditional dog collars and do NOT have "D" rings or any metal which may interfere with RF signals - Fits Models R21, R22 & R51 Invisible Fence Receiver Modules UV, rot, mildew, moisture resistant, pattern printed on both sides of material MADE IN THE USA - ECO FRIENDLY (minimal or no retail packaging)