This window operator is designed to be used with 3/8" square bars.  Torque bars are long horizontal bars that connect the left and right sides of windows to disburse the torque of cranking the operator across both sides of the window.  Many 1960s and 1970s vintage trailer windows use torque bars.  There are a number of different operators available so rely on the stated dimensions as well as overall shape to determine if this is the correct operator for your window.  

Dimensions

• Overall Height: 2 3/16"
• Overall Width excluding stem: 1 5/16"
• Overall thickness excluding rotating hub: 1/2"
• Inside dimension of projecting torque bar hub: 3/8"
• Length of projecting torque bar hub: 5/32"
• Length of smooth section of crank stem: 3/8"
• Mounting hole locations c-c: 3/4" top line, 1 3/4" top to bottom near stem edge
• Mounting hole locations from top and bottom edges: 7/32" from top, 3/8" from bottom