4mm Square Hole
Key/8 Size 8 Brass plated key generally fits Anniversary Clocks with #49 & #54 Schatz movements (The movement number is usually stamped on the back plate with a circle around it). 4.0mm square winding hole. Additionally, key generally fits all modern (since 1970) 3 hole German made movement 8 day wall and mantle clocks. Original often chrome silver in color. Measure square winding post for fit.
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