Canti.

Canti

They are not threaded and require the locking nut type of canti on older bikes. I use them on my Shimano XTR canti's and they work a treat.

Cosmetic only, compound is all the same (even the pink ones AFAIK)

If they are STX RC cantilever, the Canti style like in the picture are what you need.
In fact they also work on 1998 STX V-brakes, so probably work on older Shimano V-brakes as well.

Probably. I'm using them ("Canti" model not "threaded") on 1990 Shimano DX cantilever arms.
If your pads look the same as the ones in the picture, it's the Canti style you need.

Canti = like in the picture, with a non-threaded post. Fits most old-style cantilever brakes.

Threaded = screw thread on the post, fixed onto your brake arm with a bolt that threads on the post. Fits most newer style V-brakes (aka linear-pull brakes).

The Canti style would fit, but you would be better off purchasing a cartridge insert pad, that way you don't have to mess around as much getting toe-in etc right.

As long as your Tektro Cantievers brake blocks are the type were you can remove the pad from the holder then the standard Kool Stop V-Brake Standard Compound pads fit perfectly.

Just pull out the retaining pin, slide out the old pad, slide in the new pad and then replace the retaining pin. Don't worry if you drop the retaining pin when you pull it out, I did, there are replacements supplied with the blocks.