Reader answer. The width of a seal's backing, a maker's recommended opening, and the seal's reach describe different attributes. They are not interchangeable measurements. Likewise a catalog's option list identifies items a manufacturer offers, not what a particular installed window will accept.
Worked example 1: one AmesburyTruth product, several distinct fields
AmesburyTruth's product page for 52047 lists Pocket Width 0.275 in, Bulb Width 0.387 in, Bulb Height 0.390 in and Overall Height 0.510 in in its product highlights. Its specification table separately lists Backing/Kerf Width 0.275 in, Recommended Opening 0.310 in and Reach 0.390 in for named 52047 ordering rows. Those are different headings in a single issuer document. [E10-F008][E10-F009][E10-F010][S06]
Do not convert that example into a shop instruction. The “recommended opening” field is the product maker's recommendation for these listed rows; it is not a measured throat width of your existing frame, and it does not authorize widening or altering any channel. The listed “reach” is not the same thing as a seal's total outside height. Copy the field label with its value, unit and exact product code, rather than making a universal “0.31-inch T-slot” assumption.
| Source label for 52047 | Source value | What to record separately |
|---|---|---|
| Backing/Kerf Width | 0.275 in | Actual observed sample backing, with tool resolution |
| Recommended Opening | 0.310 in | Maker's named recommended dimension; actual receiver unverified |
| Reach | 0.390 in | Published projection/reach; installed contact geometry unverified |
| Bulb Width | 0.387 in | Outside soft-section dimension, not mounting width |
| Overall Height | 0.510 in | Source's overall profile size, not automatic installed clearance |
Worked example 2: options can change which widths are offered
Ultrafab's current Tri-Fin® webpage lists standard backing widths 0.187, 0.200, 0.210, 0.229, 0.270 and 0.310 in. On that same page, its S7 T-Loc option excludes 0.229 in while S9 T-Loc includes all six; the adhesive option is listed only for 0.187, 0.270 and 0.310 in. These are conditional published option choices, not a claim that an S7/S9 or adhesive strip fits your slider. [E10-F011][E10-F012][E10-F013][S07]
This matters because a shopper who quotes “Tri-Fin is available in 0.229” without specifying the backing type may accidentally request a combination the maker's visible option table does not list.
Non-destructive measurement worksheet
- Photograph the seal's end view and its receiver in situ; label which edge faces the glazing or frame and which direction it compresses or slides.
- Name the measured feature: backing/base, neck/stem, soft bulb, pile height, available groove opening or actual working gap. Never call them all “width.”
- Record original inches or millimeters, the instrument, its smallest readable division, repeated readings and whether the sample is crushed or stretched. Do not invent tenths or decimals finer than the tool can support.
- Put maker catalog values in a different column from the user's measurements. A used sample and an unexamined receiver may not represent undamaged design geometry.
- Ask the maker or specialist to check the exact part+backing option, direction, retention profile, material and relevant installed frame before any fit conclusion.
What the sources do not establish
Neither webpage is evidence that an existing frame has a matching channel, that the product will achieve a seal under installed compression, or that one manufacturer's item can substitute for another. A mismatch in any important base/retainer dimension means the proposed fit remains unverified; do not force insertion or modify a manufactured channel on the strength of a table. Rated, smoke-control and egress assemblies need qualified maker-specific review.
Sources and boundaries: [S06] AmesburyTruth 52047, product highlights and specifications (accessed 2026-10-12). [S07] Ultrafab Tri-Fin Weatherseal Choices , accessed 2026-10-12.