Slip Joint vs Threaded.....J Trap

I dunno where I purchased this but in my last remodel, for both the laundry sink and bathroom, I finished the RO was a female pipe thread...

From the J trap, it was slip joint to the J Trap and the extension tube to the wall was actually make threaded.

I do like this versus slip joint connection at the wall (in my mind, a threaded connection is more secure over the long run) than a slip joint. If the washer was to fail, I don't mind the leak to the floor but I would want to avoid any water on the sheetrock at all costs....

How unusual or usual is this piece I am describing. If such a animal still exisits, I would proably want to run it the same way RO when I redo my upcoming bathroom...

The standard method of connecting the P trap to the drain is with a trap adapter. These usually are included in the trap set. The adapter has male threads on the trap side.

They say a picture is worth a thousand words. I just decided to go take a pic...
Hmm...what makes me wonder what is that slight crud between the extension piece and the *outer male thread*.
I went and looked at my other sink with the same setup, shone a light on it and the metal is clean as a whistle.

A picture is worth a thousand words, a fuzzy picture is almost worthless. In the old days that was called an "L A pattern" P trap. At that time, we used them for kitchen sinks. From this and your other posts, I get the definite impression that you like to do things the "hard way".