Harley Shovelhead Chain Tensioner Mounting Kit (OEM #399920-65C)
This is the late style kit, which uses a carriage-style bolt, washer, and nyloc. The earliest style, however, utilized a hex-style nut, lockwasher, and u-shaped nut that fit behind the adjuster plate.
The "-65C" component of the part number suggests use back to 1965, but we suspect this style is most common to the Shovelhead era.
061522 Bx-1 (OS)