Hi,
My balance spring assembly looks like your Series 770. It measures 28 inches using the picture you have for measuring it. The unit measures 28inches from end to end as in your picture. On the unit it has a number: 27D. Is this a 28 inch unit or a 27 inch unit based on the stamping?
Thanks,
Art
If your balance resembles our Series 770 and it has a "27D" stamp, that usually indicated that the balance measures 27" in length. I would reconfirm your measurement again to be sure.
Thanks for your photo. This definitely looks like our Series 770. I'm not sure why it has a 27D stamp with a 28" long metal channel. It's possible yours was made by an older manufacturer who used a different rating system for the stamps. It happens sometimes.
At the end of the day, the hard facts don't lie. If your metal channel is 28", then it's 28". You don't want anything else. The only thing I'd recommend is that you weigh your sash on a scale to confirm the best S770-28 stamp option. The 28D may not necessarily be what you want, so it's best to confirm. We have a chart on the S770-28 store page that you can use as a reference.
