Need help finding out the drain cap size!

[diy_try_guy]

Hello

I need help with identifying the drain cap size for this pipe. I have attached photos of the pipe below. Can you guys please help?

Thank you for your time

 

[Twowaxhack]

Google this Apollo number I circled. Either get a cap or buy a new valve and rob the cap.

 

[diy_try_guy]

Thank you for your excellent suggestion. I am ordering it from valveman website

The part installed had 800 CWP but the one on the website is 600 CWP I am not sure it matters

Thank you again