Casement handle, think the mfg was Monarch Windows & Doors

See our 39-205 Holding Handles. This can fit on splines that are 11/32" in diameter, so check this matches your operator's spline. Note that if the gears are stripped, you will in fact need to replace the entire operator. We can help with this, but we need to see the entire mechanism including the link arms to narrow down what you need.