I am looking for a replacement of the pictured balance. I believe it is a Series 385 Sideload Channel Balance Sash Support System. It is 26" long (metal section). However, I am not sure about the bottom insert as mine is slightly different than that shown in your photo. I did not upload a photo, but the number stamped on the metal section is 25 5. To the right of this number are the letter SL perpendicular to the numbers followed by PF in smaller letter in the same orientation as the numbers. If you require further information, please do not hesitate to contact me.
Sincerely, Jason D