I replaced my bathroom sink, got a fixture without a pop-up plug. Somehow I scavenged a nice brass drain, Dearborn Brass 759-1. It has the fitting for the pop-up drain lever in its side, but not the nut or the lever. I want to plug it. It'd be nice to have a cap nut that would fit. I measure its diameter with my calipers as 27/32. Is there a standard part for this purpose?

You are taking about the side rod cover nut?

I don't know if those threads are special. But I have German faucets and US faucets and the nut threads seem different. But I never had any issue finding a new cap to fit. The only thing is I don't know if you can find a closed cap, but I know you should be able to easily find a side rod with the ball plus the cap with a hole and seal that hole with both together.

But the issue is how will you control and up and down movement of the popup stopper without a lift rod and a side rod? Are you going to remove the stopper and just leave it open?

Yes, thanks, the 'side rod cover nut'. I was hoping it was a standard thread and that someone made a cap nut that big. Even with a regular nut I may can improvise a cap.

I bought a new faucet, one without a pop-up. I almost never stop the bathroom sink, have spent more time cleaning out the mechanism than using it. I'll put a plug in it when I want to.

You would be better off using a grid strainer. This one is available from our sponsor: [www.plumbingsupply.com]

ditto

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

They have various drains to pair with faucets without a popup assembly. Some of them have a grid, some of them are push down stopper. If you have to use the pop up drain then you need to either find a closed cap, or use an existing cap that has a hole in the middle, and just cut the rod off the ball and use it to seal. May be a piece of rubber cut to fit the cap's ID could work to seal it by compression.