Thank you for the replies. The boat is an 88. I did search using deck fill, water fill, deck plate, etc. My apologies for not finding a relevant thread.
I have tried perko and seachoice and if you line up the threads you can see the original has a slightly wider thread and my thread gauge indicates an 11. I know some of the old wilcox-crittenden deck fills had a different cap and was wondering if anyone knew the make of the ones used on the 1988 Ericsons. I do not see a marking on the fill or the cap.