Key/4 3.75mm Square Hole Size 4 Brass plated key generally fits Anniversary clocks with #53 Schatz movements (The movement number is usually stamped on the back plate with a circle around it). 3mm square hole. Additionally, key generally fits Seth Thomas (manufactured 1970 to present) and many 2 hole Wall, Mantel, and Ships Bell Clocks. Measure square winding post for fit.