Vintage line stringing swivel by Pengo-Miller, size B-13 L-1/2 with a working weight limit of 3.75 tons. Line stringing swivels (also known as line pulling swivels) are used while stringing high tension electrical wires to stop them from twisting up and damaging the conductors. The stamp is legible though the body of the piece is tarnished. This is still in production and retails new for $240, but there are other vintage ones listed on Ebay for $200, $249, and $395.