Spring tensioner

Hey there. This looks like either a Series 380 or Series 385 Channel Balance. The only difference between these two balances is the 'depth' of the bottom nylon shoe as shown below. Measure your old balance's shoe depth to see what matches best. Measure the length of the metal channel, not including the nylon attachments, to determine the right length. To know what stamp option to pick, look for a stamp on the metal channel. Let me know if you have questions.

Comparison of the S378, S380 and S385 balance shoes.