The Extech DO603 Membrane Kit is a crucial accessory for maintaining the accuracy and longevity of Extech dissolved oxygen meters. This kit contains six screw-on membrane caps, a 15mL bottle of filling solution, and polishing paper, all essential for replacing worn or damaged components. Regular replacement of these parts ensures consistent and reliable dissolved oxygen measurements in various applications, from laboratory research to field testing in water bodies. The included polishing paper helps maintain the membrane's surface for optimal performance. This kit is compatible with both the DO600 and DO605 meters, making it a versatile solution for dissolved oxygen measurement needs.