Lots and lots of boats have Perko brand deck fillers. We don't. I can read "Japan" on the filler cap. And that's about it.

Is it a Perko clone? Can I buy Perko o-rings?

It is fundamentally different? What size o-rings do these fillers use?

I peeled off an o-ring and measured it as carefully as I could. It is rubbery, so exact dimensions are difficult.

I searched around and find that Dash 224 and Dash 223 were both close to what I measured.

This is what I need to save in my logs:

Dash-223

Durometer 75

We have 6 fillers. The cheap rings come in packs of 25 for $15. With a 20 year shelf-life, I can replace them every five years before I run out.

The fancy ones come in a pack of 2 for $4.00. This was handy when I didn't know what size to get.

Now I know the size. Pack of 25. Done.