Attach one of these variable angle swivels to an air tool or air hose and it’ll allow it to move more freely, or so Milton claims. The fitting allows the hose to both swivel and bend farther than a rigid coupling without kinking. It’s not mentioned in the available information, but presumably there’s a ball fitting of some type under the flexible rubber boot.
Besides 1/4″ MNPT to 1/4″ M-style plug, the swivels come in 1/4″ MNTP to MNTP, 1/4″ MNTP to FNTP, and 3/8″ MNTP to 1/4″ M-Style plug. Any of these chrome-plated variable angle swivels will run you $6 before tax or shipping.