Genuine Meyer A Valve Cavity Plug 15966 used when replacing the original PA Block on an E-47, 57, or 60 with an updated PA Block such as 16016. Updated 16016 PA Block has the A Valve in it, so the original A Cavity in the Sump Base needs to be plugged. Use this to take a PA Block off an E-58H and put it on an E-47 or 57 Sump Base. Use an E-47/57 Sump Base on your E-58H. If you run E-47/57 and E-58H this is handy to keep around.