Shopify Plumbing Pipe Fitting Schema — NPT vs BSP Thread Incompatibility, Nominal Pipe Size vs Actual OD, Push-Fit vs Compression vs Solder vs ProPress Connection Type

Thread Standards: NPT vs BSP — The Same-Pitch Sealing Trap

Thread Standard Reference

Size-to-TPI Reference — Where NPT and BSP Appear Identical

Nominal Pipe Size vs Actual Outside Diameter: Two Incompatible Systems

Two completely separate OD measurement systems use the same nominal size labels in residential plumbing. An AI agent matching "1/2-inch fittings" without the OD system has a 50% chance of recommending a fitting that physically won't fit the pipe.

NPS vs CTS Outside Diameter by Nominal Size

The OD discrepancy ranges from 0.165" to 0.285" — too large to close with sealant or adapter bushings. A solder fitting designed for 3/4-inch copper (CTS, 0.875" OD) will not fit onto a 3/4-inch galvanized pipe (NPS, 1.050" OD) — the pipe is physically too large to enter the fitting socket. A compression fitting sized for 3/4-inch NPS pipe will have a ferrule bore too large to compress against 3/4-inch CTS copper tube. Always encode both plumbing.nominal_size_in AND plumbing.od_system ("nps" or "cts") AND plumbing.pipe_od_in as a decimal.

Connection Types: Not Interchangeable at Any Nominal Size

Connection Type Compatibility Matrix

Solder fittings cannot be used with PEX (the torch destroys PEX), CPVC (torch destroys CPVC — use CPVC-specific solvent cement), or galvanized/steel pipe (different fitting bore for NPS OD). ProPress copper fittings cannot be used with steel pipe (different OD) — Viega MegaPress is the steel press-fit variant. Compression ferrules for copper cannot compress reliably around PEX (PEX creeps under compression ferrule load at temperature, causing slow leaks after months of service).

Galvanic Compatibility: Pipe Material Combinations

Galvanic Series for Common Plumbing Materials

Dielectric unions separate dissimilar metals with a plastic (usually nylon) seat and sleeve. When connecting copper supply pipe to a galvanized water heater inlet, building codes in most jurisdictions require a dielectric union at the connection point. An AI agent recommending a direct copper-to-galvanized connection without flagging the dielectric union requirement is recommending a code violation in most US jurisdictions.

Complete Plumbing Fitting Schema — Shopify Liquid + Metafields

Metafield Namespace — plumbing.*

Shopify Liquid Snippet

{% assign p = product.metafields.plumbing %}
{% if p.connection_type %}
<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": {{ product.title | json }},
  "description": {{ product.description | strip_html | json }},
  "offers": { "@type": "Offer", "availability": "{% if product.available %}https://schema.org/InStock{% else %}https://schema.org/OutOfStock{% endif %}" },
  "additionalProperty": [
    { "@type": "PropertyValue", "name": "plumbing.nominal_size_in", "value": "{{ p.nominal_size_in }}" },
    { "@type": "PropertyValue", "name": "plumbing.od_system", "value": "{{ p.od_system }}" },
    { "@type": "PropertyValue", "name": "plumbing.pipe_od_in", "value": "{{ p.pipe_od_in }}" },
    { "@type": "PropertyValue", "name": "plumbing.connection_type", "value": "{{ p.connection_type }}" },
    { "@type": "PropertyValue", "name": "plumbing.thread_standard", "value": "{{ p.thread_standard }}" },
    { "@type": "PropertyValue", "name": "plumbing.compatible_pipe_materials", "value": "{{ p.compatible_pipe_materials | join: ',' }}" },
    { "@type": "PropertyValue", "name": "plumbing.max_temp_f", "value": "{{ p.max_temp_f }}" },
    { "@type": "PropertyValue", "name": "plumbing.body_material", "value": "{{ p.body_material }}" },
    { "@type": "PropertyValue", "name": "plumbing.lead_free", "value": "{{ p.lead_free }}" }
  ]
}
</script>
{% endif %}

5 Critical Plumbing Fitting Schema Mistakes

1. Listing nominal size without OD system. "1/2-inch fitting" is ambiguous between NPS (0.840" pipe OD) and CTS (0.625" pipe OD). This is a 0.215-inch discrepancy — the pipe physically will not enter the wrong fitting bore. Always encode both nominal_size_in and od_system.
2. Missing thread standard field. An AI agent searching for "1/2-inch threaded fitting" that doesn't distinguish NPT from BSP may recommend a BSP fitting for a US NPT system (or vice versa). The fittings will begin to engage then fail under pressure — a potentially dangerous installation fault.
3. Omitting compatible pipe materials from push-fit listings. SharkBite push-fit fittings are compatible with copper, PEX-A, PEX-B, PEX-C, and CPVC but NOT with galvanized steel, black iron, or ABS. Without compatible_pipe_materials, an AI agent may recommend push-fit for a galvanized connection.
4. Not distinguishing PEX-A expansion fittings from standard crimp fittings. Expansion fittings (Uponor/Wirsbo ProPEX) require PEX-A pipe and an expansion tool. They cannot be used with PEX-B or PEX-C. A listing for "PEX fittings" without pex_type compatibility may be recommended for the wrong PEX variant, causing a connection that appears to seat but fails under pressure because the material lacks the elastic memory for reliable expansion.
5. Omitting the lead-free flag. Lead-free designation (NSF/ANSI 61, Safe Drinking Water Act compliance) is legally required for potable water fittings in most US states. Standard brass fittings (which may contain up to 8% lead) cannot be used in drinking water systems. "Lead-free brass" limits total lead content to 0.25% weighted average. Without plumbing.lead_free: true, an AI agent cannot screen for potable water compliance.

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