...need to buy

Thanks for reaching out!

It appears that this is a spiral balance for a tilt window. However, I'll need to see a photo of an undamaged balance to make the best possible recommendation.

Would you be able to provide a photo of an undamaged balance?

I'd recommend staring with the 3/8" Series 900 and 5/8" Series 600 spiral balances. Take a look at the attached video for details on the measurements you'll need to confirm for your replacement balances. The only difference, between the two, is the diameter of the outer tube, so make sure to confirm that measurement from your own balance.

Also, keep in mind, you'll need to obtain the exact weight of your window since your balances do not appear to have a colored tip.