This is a accessory drive belt to fit some 1955-1988 vehicles.
Dayco #15560

Fits:
Buick 1975-1987
Cadillac 1958-1983
Chevrolet 1955-1988
Oldsmobile 1968-1988
Pontiac 1963-1987

Engine sizes: 231cid V6 (3.8L), 252cid V6 (4.1L), 301cid V8 (4.9L), 350cid V8 (5.7L).

Belt measures:
Top Width: .44" (15mm)
Length: 56" (1422.40mm)
Circumference:56.57" (1436.88mm)