Truth Entrygard Dual Arm Operator. We would expect you to find 20810 or 20544 on the linkage arm, which measures 4-7/16" overall length. This is the most common size we find in use. Other common numbers we would expect to find are 31538, 31539, 30841, 30842, 30472, 30470, 20810, or 20544. Also known as a TH-24008 or TH-24009.
For offset up linkage arm, order Wi1510.
To determine hand of operator, if your sash lock (window lock), is on the left, you would use a left hand operator. And if your sash lock is on the right, you would order the right hand operator.
Part # Hand
WI1561R Right Hand
WI1561L Left Hand
Truth Entrygard Dual Arm Operator