Harley Primary Chain Tensioner. I'm not sure what model it fits, but I bought it for my 1980 XLCH and never installed it.  It is used but in very good condition. Tension is from spring steel plate that is positioned under the wear pad (like shown in one of the pictures). It came to me used in the box in the picture, but it does not match the picture - possibly a re-used box by the person I bought it from? Buyer is responsible for fitment on their bike.