part number

I am seeking the plastic part . that goes on the top of the "top slide" for a bi folding door.
most of the ones i viewed have a round wheel at the top , but i am seeking a hardward piece for an older bi fold door which at the top of the slide has a small"square " plastic piece which allows the door to slide along the metal track.

thanks
i think thats the exact one.
appreciate it

Mike
one additonal question. these caps are hard to get into the "track"
the pic you have posted here --- am i correct in assuming the top part of the nylon tip as shown , when i place it in the metal track will be reversed from the position of the picture as shown.
that is the smaller part will be at the top of the track( as its impossible to fit the larger piece into the track. not wide enough

THANKS. I am starting to lose my religion over getting the tips into the metal tracks.
common sense would seem thats the way most should be made but the nylon square ones , do not snap in. I've cut the top part back , screamed at it , cursed it and am relieved to finally find the one you pointed out.
Terry T
T