Felt Formal Top Hat that includes an adjustable strap that secures under pet's neck. 5 sizes -: XXS - 2 in ID/3 in OD, XS - 2-1/2 in ID/4 in OD, S - 3 in ID/5 in OD, M - 3-1/2 in OD, 5-1/2 in OD, L - 4-1/2 ID/7 in OD Measurements