trap adapter male threads the same or different from MIP threads?

[BobJacobs]

I am replacing a double his/her sinks with a single sink in the bathroom. Therefore one of the drains is no longer needed.

I would like to cap it, but want to keep the option open to use it if necessary, for example, as an access point to snake the line without needing to take the sink's trap apart.

My original plan is to cement on a cleanout adapter with a cleanout plug.

That doesn't work because the stubout has a 1-1/2" trap adapter cemented on, and only the male threads are exposed. Not only that, using a flashlight into the drain behind the wall, that trap adapter is a "street" trap adapter cemented into the hub of a 1-12/" PVC elbow. I would prefer to not tear into the tiled wall.

My question is, the male threaded end of a 1-1/2" trap adapter, is it compatible with regular 1-1/2" FIP threads? Can I thread on a 1-1/2" PVC threaded cap or 1-1/2" female adapter? Or are those special compression threads?

If they are not compatible, do they sell a cap for trap adapter - just like the nut but without the opening for tubular insertion?

 

[Breplum]

They are normal threads, just typically a bit shorter when in the form of a trap adapter.
A threaded plastic cap will not fully seal without a lot of Teflon wraps. A less clean option is a test plug, which will seal readily and fully as well.

 

[Sponsor]

 

[Reach4]

This is the Sioux Chief 235-QP. https://www.supplyhouse.com/Sioux-Chief-234-QP-1-1-2-QuickPlug-Trap-Adapter-Test-Plug This is used with a regular slip washer

1 ½" Trap Adapter Test Plug

• Eliminates traditional test plugs
• Allows you to fit the trap adapter tightly against
  the wall for a clean, professional look
• Requires use of standard or Drip-Free ™ 1½" slip joint
  washer

I mostly see these pictured as black, but occasionally white. I don't see a separate part number, so this may reflect a change in how they are made. I snipped the above drawing from https://www.southernpipe.com/ASSETS/DOCUMENTS/CMS/EN/SC61357Y_1.pdf page "230", and it has a white picture. That catalog appears to be from 2007.