21" Caldwell Series 300 5/8" Channel Block & Tackle Window Balance - Stamp 20-4

I ordered two of these along with a selection of end pieces and a rivet tool to make sure I would have the correct ones. As it turned out, I was lucky - the end pieces already fitted were exactly the correct ones for my window. They went in without any bother, and no tools needed - there are instructional videos on YouTube which taught me how to.Only one of the two two sides was broken in my window, but I replaced them both anyway, given the very reasonable price. I'm glad I did as the window now operates more smoothly and easily than it did before it broke. I guess these things do wear down over time.My only regret is that I put off doing this for a couple of years, expecting it to be a difficult or expensive repair, probably needing to call in an expert. It wasn't it was easy.Make sure you get the right size. There should be some numbers stamped on the old ones, and there are web sites which tell you how to interpret those.

Worked with no problem.

Quality it’s great and fit perfectly to the window I highly recommend

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The one I pulled out of our Milgard window had little wings that guided the window in the frame. I couldn't find any with this spec and the wings. This went in smoothly and worked perfectly.

Old string broke on my window so I ordered two of these so both sides would have the same tension. The small pulley mechanism is plastic instead of metal like my old ones and broke on first try for one of them. So now it is uneven tension I thought would avoid.

So easy to install! Wish we would have done it sooner!

When the single hung windows of my house started to give trouble I thought that I would have to replace the complete window. Luckily I discovered that a new pair of window balances will make the window work like new.Highly recommend this purchase.