You’ve found a number stamped on your window balance. Finally, something you can search for. But the results bring up several parts that look similar, and suddenly that number raises more questions than it answers.
Window balance markings can help identify the size and weight capacity you need, but their meaning depends on the balance system. They are a useful starting point for finding a replacement, rather than a universal part number.
What the first numbers can tell you
On many common block and tackle window balances, the first two digits relate to the length of the metal channel. A stamp reading 1440, for example, commonly corresponds to a channel measuring 15 inches. That difference is intentional: in this marking system, the first portion of the code is one inch shorter than the channel itself.
Commonly corresponds to a 15 inch metal channel in this block and tackle marking system.
Identifies a rating to check against the correct series and length. It does not mean 40 pounds.
Always confirm the measurement using the metal channel only, leaving out the plastic guides and projecting attachments. If your measurement includes a fraction of an inch, check with us before choosing a replacement. Our guide to measuring block and tackle window balances shows where to start and stop your measurement.
The weight code is not a weight in pounds
The remaining digits help identify the balance’s spring strength or supported sash weight range. The “40” in 1440 does not mean the balance supports a 40 pound window. It is a rating code that must be checked against the listing for the correct balance series and length.
Even the same complete stamp can appear with different weight ranges across different series. For example, WHD’s 28 inch Series 400 listing assigns stamp 2740 to a sash weight range of 19 to 26 pounds, while the 28 inch Series 450 listing assigns it to 20 to 27 pounds. The series matters just as much as the number.
A matching stamp does not confirm a complete match. Check the balance style, dimensions, attachments, and listed sash weight range before ordering.
Different balance styles use different clues
Other balance styles use different identifying details. Coil balances may have markings on the spring or housing, while spiral balances require attention to the tube dimensions, tip color, and window application. Applying a block and tackle stamp rule to another balance type can lead you toward the wrong replacement.
Start by identifying the type of balance you have, then compare its markings and physical features with the relevant product information. For spiral balances, our spiral balance measuring guide explains the details to record.
What to gather before ordering
Photograph the full balance, both ends, and every readable marking. Record the dimensions and keep the original part available for comparison. If the stamp is worn away, those photos and measurements become especially useful. The sash weight may also be needed to confirm the appropriate rating.
Found a stamp but still unsure?
Window Hardware Direct can help you work through the identification process. Send us the photos and measurements you have so we can help narrow down a compatible replacement.
Get Help Identifying Your Balance