Plastic screw-on cap holds the calf nipple in place on a standard nursing bottle. Works with the Little Giant Screw-On Calf Nipple (Item Nos. 93SCN and 93PK, each sold separately). Threads fit the Little Giant 2-Quart and 3-Quart Nursing Bottles (Item Nos. 93CB and 9303CB, each sold separately). 2.5 inch diameter by 0.625 inch high.