channel balance identification & quantity; support bracket for upper sash

We are repairing a window with 1 broken channel balance. It is an aluminum frame single hung window, approximately 31" wide x 67" tall. There is a faint stamp on the channel balance track which looks like it says: 3160 ojBSI

There are two slots for the metal hook from the channel balance, but only one in use.... Is it possible that such a heavy window should have two channel balances on each side of the sash? (I have not weighed the sash, but it is quite heavy to lift without the channel balance, and one of the two channel balances broke when the window was only a few years old.)

We are wanting to make sure we order the correct replacements, and should we get two (one for each side of sash), or four (2 on each side of sash, even though that wasn't what was there before)?

There is also a plastic support bracket that holds the upper sash in the closed position, which is broken. We are wondering if there is a replacement for this? See final image.

Thank you for your help!!

Hi, I submitted a question about a channel balance replacement, but I'm writing with some revised info b/c I read the stamp wrong before.

I've measured the existing balance & I'm pretty sure it's a SERIES 385. Now I see that the stamp is related to its weight bearing. Looking at it more closely, I'm pretty sure the existing stamp says "3130". (See new picture.) HOWEVER, I'm fairly confident that these were inadequate for the load of the sash. I don't have a means to weigh the sash, but it certainly seems to be more than 23 pounds! (This is an aluminum frame double-pane window, about 31" wide by 67" tall overall.) So I'd like to get a stronger rated pair of balances, but I'm worried about overdoing it & having the window want to stay open. Any suggestions?

Thanks again! Your website has been tremendously helpful!

Thank you for the feedback! I'll order the side balances. Since it's close to the next weight category, would it be okay to order the next spring weight up (3140)? All of the existing windows of this size are difficult to open (and have been for some years), so I'm wondering if a stronger spring would help. But, we don't want to make it difficult to close!

Regarding the fitting, it cant be removed without uninstalling the upper sash, which I don't want to do in the middle of winter unless we have a replacement part! I've taken some better pictures of an unbroken one on another window. Overall length is about 4". It operates similarly to a slide latch on a storm window, but it's on the exterior of the window. Seems to be intended to help keep the upper sash from drifting down, so that it's easier to latch the two sashes together.