This is a used short window regulator roller track taken out of a 1957 Chevy 4 door 210 sedan.  The interchange I found for this shows it will fit the '55-'57 Chevy and Pontiac 4 door sedans (post cars) and 4 door wagons.  This will not fit any 2 door model or the '56-'57 4 door hardtop (no post cars).  This one came off of the passenger's (right) front door.  But, this will fit either the driver or passenger sides and will also fit either the front or rear doors.  This is the stationary piece that screws to the door and doesn't move with the window.  One of the rollers in the window regulator goes in this piece. The threads on the captured nuts still look to be in good condition and it comes as shown with the two mounting screws.  It has been sandblasted and primed, but it still needs to be either painted or powder coated before being re-installed.  It has some pitting from the rust, but doesn't look bad - see pictures for close ups.  It measures 7-1/4" long x 1" wide and the center to center on the screws is 6-1/4".  Please contact me if you have any questions and thanks for looking.