There are several styles of rack operators used in vintage trailers.  The best way to pick the one for your trailer is to use measurements of your old operator and confirm them against the available models.  Included accessories allow you to customize the fit for your window, but the overall size and mounting hole location will be important.  Also, consider whether the end of the rack has the proper attachment feature for your existing window parts. 

Specifications: 

• Cast zinc housing: 2-1/2" x 1-1/3" x 1/2"
• Cast zinc reversible rack with 3-3/4" travel distance
• Zinc plated steel flat link bars: 3-1/2", 4" and 5"
• Mounting holes: 2-1/8" apart from top to bottom and 5/8" and 1" from the back edge parallel to the rack
• Bar linkage stud with e-clip
• Each flat link bar has a threaded hole & screw, and e-clip
• Includes 4 mounting screws with stamped nuts
• Black plastic handle with zinc-plated screw
• Distance between mounting holes