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NGP automatic door-bottom cutting limits: why catalogues and installation sheets disagree

Short answer: There is no single safe “NGP automatic door bottom can be shortened by X” rule . A published NGP catalogue describes a broad family of…

Short answer: There is no single safe “NGP automatic door bottom can be shortened by X” rule. A published NGP catalogue describes a broad family of heavy-duty automatic bottoms with an allowance that differs from NGP's model-specific 680 installation sheet and current 680DKB-48 listing. The correct response is to identify the exact product code, compare its matching current cut sheet and installation instructions, and request written clarification before field work—not select the largest allowance found anywhere. [N02, N06, N08]

The real document conflict, shown openly

The NGP Gasketing & Automatic Door Bottoms catalogue, code NGP-CAT-GAS-0424-A, printed page G39, carries a general heavy-duty surface family statement: units 36 inches and longer may be cut up to 4 inches in the field, and shorter units should not be field-cut. The same page groups multiple 420, 520 and 680 series drawings. [N06]

However, the separately published 680 product sheet NGP-GKT-680-PCS-0626-A and 680 installation instructions labelled 9.25 give different length bands: 12–18-inch units: no more than 1/2 inch; 20 inches and up: no more than 1-1/2 inches. NGP's current 680DKB-48 product HTML repeats the narrower two-band wording. [N02, N04, N08]

The 222NA-36 product HTML and 220, 222, 229SS instructions labelled 8.25 also repeat those 1/2-inch / 1-1/2-inch bands for their stated product family. [N01, N07]

This is a source-version / product-scope discrepancy, not permission to adopt either rule without confirming. The generic G39 table has different breadth than the dedicated 680 instructions. No claim is made here that one text has been officially superseded or that a particular shipped specimen can be safely shortened by either amount.

Three separate dimensions often get conflated

  • Listed or nominal order length: a SKU suffix such as -48 is part of a product designation, not a measured existing door opening. [N02]
  • Permitted reduction of a particular assembled unit: a specific manufacturer instruction controls whether any field sizing is permitted and under what constraints. Different series or document editions may disagree. [N07, N08]
  • Measured clear distance at the installed opening: the end condition differs for a single door versus a pair; this is a site measurement, not an inferred specification from a nominal SKU. NGP's installation sheets make that distinction, but the actual work belongs to a qualified installer when the opening is regulated. [N07, N08]

Before ordering or authorizing service, do this

  1. Photograph the complete factory label and stamping. Write down exact model, suffix, nominal listed length, finish, handing, and any special option; don't rely on a faded silhouette.
  2. Identify the source document's product family and printed code, not just a copied quote. Keep the G39 family catalogue statement separate from the 680 or 220-222-229SS instructions.
  3. Record your opening's type: single vs pair, threshold condition, the existing bottom's closed position and any interfering floor material. A photograph is more valuable than an unsupported estimated clearance.
  4. Contact NGP or the specifying dealer with the two conflicting exact citations: catalogue NGP-CAT-GAS-0424-A page G39 and the matching 680 instruction 9.25 (or relevant current sheet). Ask: Which limit applies to my exact ordered unit and production revision? Is a factory net-length order preferred? What service bulletin or written direction resolves the difference?
  5. If the door is labeled for fire/smoke, is an egress door, or is under an accessibility or acoustic performance requirement, do not cut, drill, reverse or substitute parts based on this informational comparison; obtain approval through the door manufacturer, listing/authority and qualified hardware contractor.

When “do not know” is the useful answer

If you have only the broad catalogue photograph and no exact unit ID, a universal numeric cutting allowance is not verified. That does not mean the unit is unusable; it means first-party model-specific information is missing. Ask for a factory-sized replacement or documented service solution rather than guess from a nearby series. Also avoid treating the site's general measuring protocol as a manufacturer-cutting guide.

Original documents

This guide provides no field-cutting instructions, installed safety certification, or authorization to modify a door assembly.

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