need help identifying this part

Hello! This part is called a channel balance. Your specific configuration is a special "extended travel" channel balance, named for its unique block and tackle system. We do sell these, but it has to be a custom order.

Before we go any further, please show me a clear photo of the metal hook at the end of the cord. I will also need to know how many you wanted to buy. Lastly, please verify how long the metal channel is by itself. Do not measure the nylon fittings, just the metal channel. Based on your old stamp of 1930, it should be 19-7/8" long.

Thank you! That picture of the clip is very helpful. Now I just need you to answer the other questions I had in my previous post. Once I have all the requested data, I can email you a purchase link and price quote that you can use to place an order on our site.

Thanks for getting back to us. We unfortunately don't sell these with a 21-3/8" length. We can only provide them in 7/8" length increments, such as 19-7/8", 20-7/8", 21-7/8", and so on. Can you verify that size for me? If you are positive that it is 21-3/8", then it is not something that we can sell. 

You also mentioned that you need two of the 21-3/8", but you didn't say how many of the 19-7/8" you required. I need a count for every balance you want to buy before we can start.

That's a different measurement than the two we already talked about. You had originally requested a 19-7/8" balance, as shown in your photos. You then requested two of the 21-3/8", which isn't a size we sell, and then two of the 21-7/8", which wasn't mentioned until now and isn't in your photos that I can see. As for the 19-7/8", I still have no idea how many you needed to buy.

At this stage I'm very confused as to what you need. These are special order balances that we have to custom make from scratch so I really need clarity from you here.

What length balance did you want to buy? If you need a balance measuring 21-7/8", can you tell me what the stamp reads? Can you also confirm that it's identical in design to the photos you submitted originally? If it differs in any way other than size, I need to see it. 

Thanks for clarifying, Ed. If the window is drifting down when it's fully opened then changing the length won't do anything to fix it. That has more to do with spring calibration. In addition to that, using a longer balance than what the window was designed to take means that it will stick out of the bottom of the sash, which will prevent you from closing it all the way. Unless you have strong evidence that the currently installed balances are the wrong length for the size of the sash, I wouldn't advise using a 21-7/8" for this application. These are very precise systems and even being a fraction of an inch off will render the balances inoperable, let alone a whole 2" difference.

The way these work is the balances provide constant upward force that counteracts the downward force provided by the weight of the sash. If the upward force is less than the downward force, the window will drift down, similar to what you describe.

How long have these windows been installed? It's more likely that the springs are just worn out, which happens with age and constant use. Balances get weaker over time and are unable to hold up as much weight as they used to. For reference, two of these balances with a 1930 stamp are designed to hold 12 through 14 pounds. After ten or fifteen years of use, that number will drop. 

Does your window sash fit in that weight range? If not, how much does it weigh, precisely?

If you are 100% positive beyond any shadow of a doubt that this window was designed to take a 21-7/8" long balance, then I will need to know the weight of the sash anyway. In that scenario the spring calibration would have to be re-calculated from scratch. 

Okay, this is starting to make more sense now. Thank you again for the clarification. So, to sum up the issue at hand, you have a handful of replacement windows of varying sizes, and in one of these cases the balances you received to get it operational again failed at keeping it open.

We're on the right track. In that case what we need to do is calculate the exact size you need. There is a method to do that and I think we should use it so that there is no room for doubt. All I need is the height of the visible glass (not the frame, just the glass) for the sash that the balances support. That will tell me what length you require.

I also still need the exact weight of the sash. Since we're changing the length, and since the balances that were used in it weren't even right to begin with, then we have to make sure this spring is calibrated properly. If we don't do that then it's not going to function. Please give that weight to me down to the ounce.

Based on your description of the issue, it still sounds like a weight problem to me, not length. These two details will allow us to know exactly what to build you.

Thanks, Ed. Based on that glass size I'm thinking it should be more like 20-7/8". The rule of thumb is to add an inch to the glass height. This rule has served me well over the years though I should stress that it is by no means universal. It's also off by a few eighths of an inch in your case, but at this stage this is the closest size that I can figure.

Assuming you need the 20-7/8" option, you would then use the 2030 stamp option. Two balances with this option carry 12 through 15 pounds, which should be perfect for your sash weight.

I'll email you a purchase link and price quote right now for two balances made with this configuration. They'll have the same top and bottom fittings as your original, as well as the same hook, but will be 20-7/8" long and have a 2030 stamp. You can use this link to add the balances to your cart.

I have to stress once again that these are not a guarantee. This is an educated guess at best. Custom balances are non-refundable, so you will have to decide whether you want to take the risk on it or not. If I were you, I would try to get in touch with the company who supplied the wrong balances to begin with and see if they can fix the original mistake. Who knows, you may get a couple free parts out of it. In the meantime, I'll email you that purchase link. You can expect that soon, I just have to write it up.