5 cup, square top glass blender jar. Replaces Oster square top glass jars. Fits most Oster blender models using a 5 cup jar with a square top. Fits most Oster Kitchen Center models. This is the most common Oster jar type. All Kitchen Centers use this type of jar. This will fit most Oster blenders, but if your is a VERY old model (40 years old), using a 4 cup jar or a new model using a 6 cup jar, your lid will not fit and you may need to purchase the OS-060 lid and cap. THIS IS NOT A GENUINE OSTER PART. The INTERIOR of the top of the jar measures 4" x 4".