Looking for proper replacement balance

Question

This is a Lawson window with metal part of balance measuring 36" with a width of 1/2". Number looks like 3520 BSI. Looks like an S380 or S385? How do I determine whether it is a 380 or 385... I'm a bit confused as to what measurement on the foot determines which one it is. Thanks.

Bob · Accepted Answer

Thanks for posting. The difference between the Series 380 and Series 385 is the depth of the bottom nylon shoe, or the measurement from 'heel' to 'toe'. The diagram below illustrates this. Measure your old balance's shoe in the same way to determine which you need. Let us know if you have further questions.

Comparison of the S378, S380 and S385 balance shoes.