Right hand straight arm casement crank with handle, no markings, original window from approximately 1976

I when I uploaded the photos they were fine, when I downloaded them 2 turned black (?) very old window, arm actually fell out of the crank portion. Arm is 9 1/2" from middle of arm button to middle of circle in crank wheel. Platform that screwed into base of sill has 4 screw holes and is 4" wide. I know this is a long shot, but I appreciate your help.