Vinyl Window No Markings

The hardware you're showing me is called a coil balance system. Coil balances are precisely calibrated spring mechanisms that go on either side of the window and keep the sash up when you raise it. They produce a constant force that's always counterbalanced by the weight of the sash, hence their name: "balance."

Yours in particular is an older style that isn't made anymore, but we can still help. Assuming you only needed the coil spring itself, you can use our Series 190. You'll note that there are many options for this coil so you'll need the stamp printed off the old one to confirm the best match.

As for installation, you actually do have a slot in your track. I can see it in your fourth and fifth photos. It's not a lot of clearance but it should suffice. 

Sure, are you talking about the clip/cover you show in your last two photos? That's our 15-186. You'll also want a new 15-182 bushing to help hold the spring to the clip.

Sorry for overlooking that detail. You can use the S190-840 in that case. That should work perfectly well.