Yes, both caps are approximately 2 3/8″ inside thread diameter. They are NOT interchangeable. Look closely at the threads. 602-5321(middle photo) has a rounded thread. This is the current style. The older cap(bottom) 602-5301 has a much sharper angled thread. The change occurred in about 2010. If you can not remember what shape the old drain cap was round or hexagon you will need to examine the threads on the sand tank. Both caps require the same o ring (805-0224). All these parts are available at http://www.waterwayparts.com
IN 2021 BOTH REPLACEMENT CAPS WERE PRODUCED IN THE HEXAGON SHAPE . THE ONLY DIFFERENCE IS THE TYPE OF THREAD. AGAIN THEY ARE NOT INTERCHANGEABLE.
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