How to tell S351 and S390 channel balances apart
Check the bottom shoe's front-to-back depth. The S351 series reference uses a 1-inch shoe; S390 uses a 1-1/8-inch shoe. Both use a non-winged top guide and non-winged bottom shoe, so wing shape alone will not separate them.
This comparison is for common non-tilt, nominal 1/2-inch channel balances. “S351-like” and “S390-like” describe a likely fitting configuration—not the identity of your original part or a guaranteed replacement.
What stays the same, and what changes?
| Check | S351-like | S390-like |
|---|---|---|
| Top guide | Non-winged; compare with 19-002 | Non-winged; compare with 19-002 |
| Bottom shoe | Non-winged; compare with 15-002 | Non-winged; compare with 15-001 |
| Bottom shoe depth | 1 inch | 1-1/8 inches |
These numbered fittings identify the parts used in the supplier's S351 series and supplier's S390 series. They are references for comparison, not universal OEM standards.
Measure the difference on the removed balance
- First confirm that the window is non-tilt and the metal channel is nominally 1/2 inch. Inspect the top and bottom plastic fittings. If either has side wings, this particular comparison does not identify it.
- With the balance removed, measure the bottom shoe from heel to toe—front to back. The relevant difference is only 1/8 inch, so do not estimate it from a distant photo. If a wing or edge is broken, record the uncertainty.
- Separately measure the metal channel length without either plastic fitting. Record the complete stamp and compare the entire fitting shape and attachment details with the seller's specifications.
Need a closer measurement walkthrough? See how to measure a channel balance. For a side-by-side fitting check, print the shoe-depth and fitting field reference.
Why the stamp cannot choose the series
A stamp can help identify spring strength or calibration. It does not tell you whether the bottom shoe is 1 inch or 1-1/8 inches deep. Two balances with the same stamp can use different shoes. See the stamp-code guide if the marking is hard to interpret.
When the answer should remain unknown
Do not choose either series if the top or bottom fitting cannot be checked, the shoe is damaged or falls between measurements, or the channel style differs. The Finder can give a review-focused result instead of forcing a match. Even when the fitting pattern agrees, verify metal length, hole locations, spring strength and the seller's full specifications before ordering.
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