BSI 1420
Hey there,
Thanks for writing in! Your balances appear to be either the Series 380 Channel Balance with a 1" shoe or the Series 385 with a 1-3/32". To confirm the correct series, you'll need to be sure to confirm the depth of the shoe. There is a chance that it could measure 7/8". If so, please let me know as these will need to be a custom assembly.
I believe the balance you have might have been cut from a longer balance. The 1420 stamp indicates that the metal channel should measure 15". However, I do see in the photos that these balances do appear to measure 12". That said, please double check the length of just the metal channel to confirm that it is 12".
I will also need to know the exact weight of the sash especially since your balance appears to have such an irregular stamp.
Please feel free to reach out with any questions you might have.