window single hung part

Hello looking for a part this goes on the window frame is a small little peace that helps the window stay in track cant seem to find them anywhere any subjections or do you have this parts this goes on the side of the window that opens up it helps to balance window and keeps it in track tights let me know what they are called and if you have them how much there is other ones that just clip on the edge of window fame either one will work thank you!!