Grigg,
The two biggest makers of fire ladders are Duo-Safety, and Alcolite. Most likely, you have a Duo-Safety. Further, there are two styles: solid beam, and truss. The truss-sided ladders are lighter yet stronger, and drew a premium. By far the most common size extension is a 24-foot, the minimum size extension specified for pumpers by NFPA for years. Retracted, measures at about 14 feet.
Take care of it - they don't make 'em anymore. (OK . . . in California, they do, but that's about it.)
-Michael
