**VERY IMPORTANT!** *EACH and EVERY set comes with a SAFE BabyWearing Checklist. If this is missing from your package, you may have ordered unsafe/knockoff rings made in China and sold by an impostor. These original SlingRings are made, packaged and shipped in the USA. Both SlingRings and Lil' Eco are family businesses, with Work From Home Mom's that support Attachment Parenting and safe Babywearing. The Rings come in a wide variety of colors, in either Aluminum (Lead and Nickle Free) or Nylon (Phthalates-Free) and the 5 sizes range from super mini to Large, insuring that you always have the perfect slip-free size for your carrier. All rings are measured from the inside edge to the other inside edge. This is their inner diameter. The nylon rings are SMALL 2 1/4"(5.7 cm), MED 2 5/8" (6.7 cm), LARGE 2 7/8" (7.3 cm) and are 0.4" (1 cm) thick. The aluminum rings are SMALL 2" (5 cm) MED 2.5" (6.4 cm), LARGE 3" (7.6 cm) and 0.25" (.64 cm) thick.