I need that plastic part to fix my window

I am afraid this is an old Simonton pivot shoe and coil balance setup that is no longer made. The Certainteed 15-192 shoe looks similar, but it does not fit Simonton windows correctly. You may be able to get it to fit if you rub down the alignment ridges on its face, but customers have had very mixed reports as to whether that works. 

We have a substitute solution. You can replace the shoe with an all-new 15-259, but it will require replacing other hardware as well, including the old coil springs with the Series 159. The video below explains.