It appears that 26-157 (RH) and 26-158 (LH)are the correct parts. These parts mention Better Bilt. Can they be used on Gapco window? Looks identical.
Paul from SWISCO responded:
March 8, 2013
Good afternoon. Thanks for contacting us. It's hard to tell what will work for you without seeing your part removed from the window, and without more dimensions. I'm not sure if Gapco uses our 26-157 & 26-158. Compare the measurements and let us know if they differ in any way.