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No-hub couplings

Entry in Joining methods · Updated · Written by the Know Your Pipes editors from the sources listed under References

A no hub coupling is a sleeve-type coupling that joins two plain spigot ends of hubless cast iron soil pipe or fittings, made of an elastomeric sealing sleeve inside a stainless-steel shield and clamp assembly.[1] It is the usual joint for hubless cast iron drain pipe in drain, waste and vent systems.[1]

The couplings are made to CISPI 310, published by the Cast Iron Soil Pipe Institute, and to ASTM C1277, which covers shielded couplings for hubless cast iron pipe and fittings made to ASTM A888 and CISPI 301.[1][2]

1 Construction

The sealing sleeve is a one-piece molded part meeting ASTM C564, with neoprene (polychloroprene) as its main elastomer; inside it is an integrally molded center stop that both pipe ends butt against.[1] Over the sleeve sits a corrugated 300-series stainless-steel shield with stainless bands and a tightening screw for each band.[1] CISPI notes the sleeve cushions shock and vibration and that the coupling is designed to allow normal expansion, contraction and deflection of the piping.[1]

Bands per CISPI 310 coupling
Pipe sizeNumber of bands
1-1/2, 2, 3 and 4 in2[1]
5, 6, 8 and 10 in4[1]
12 and 15 in6[1]

Couplings for heavier service are made to ASTM C1540.[3] One cast iron maker's warranty requires its hubless pipe to be joined only with shielded couplings to CISPI 310 and ASTM C1277 certified by NSF, or with heavy-duty couplings to ASTM C1540, and excludes unshielded couplings.[6]

2 Installation points

CISPI's suggested procedure seats both pipe ends against the center stop and tightens the bands with a calibrated torque wrench set at 60 lbf-in (60 in-lb), or the higher torque a coupling maker specifies, tightening bands alternately so the shield draws up evenly.[1] Horizontal hubless pipe is supported at every coupling, with the hanger within 18 in of it.[1] These are suggestions in a non-mandatory appendix; the coupling maker's instructions and local code govern.[1]

3 Transition couplings

Related transition couplings join drain pipes of different materials, for example where PVC or ABS drain pipe meets cast iron. ASTM C1460 covers shielded transition couplings for joining dissimilar DWV pipe and fittings above ground, up to 10 in.[4] ASTM C1173 covers flexible transition couplings for underground drain and sewer pipe of similar or dissimilar materials and sizes.[5] See transition fittings for other material changes.

Supply houses list these couplings by size and type; PlumbingSupplyAndMore's no-hub fittings category (PlumbingSupplyAndMore has the same owners as this reference) is one example.

Video

The cast iron pipe trade body shows how a no-hub coupling's gasket and steel bands seal two pipe ends. From the Cast Iron Soil Pipe Institute channel; nothing loads from the video site until you press play.

See also

  • Transition fittingsAdapters, couplings and unions that join pipes of different materials or size systems, from CPVC-to-brass to plastic-to-cast-iron.
  • ABS pipeBlack acrylonitrile butadiene styrene drain, waste and vent pipe; solvent-cemented with ABS cement and used much like white PVC DWV.
  • Cast iron drain pipeGray iron soil pipe for drain, waste, vent and sewer lines, made in hub-and-spigot and hubless (no-hub) forms.
  • Push-fit fittingsFittings that seal by pushing tube into an O-ring and locking device; covered by ASSE 1061 for PEX, copper, CPVC and PE-RT.
  • PEX crimp ringsCopper rings squeezed around PEX over a ribbed insert fitting; made to ASTM F1807 or F2159 and checked with a go/no-go gauge.
  • PEX clamp (cinch) ringsStainless steel bands with a tab, closed by a ratcheting tool over PEX insert fittings; an ASTM F2098 alternative to copper crimp rings.

References

  1. Cast Iron Soil Pipe Institute, "CISPI 310-20 Specification for Coupling for Use in Connection with Hubless Cast Iron Soil Pipe and Fittings" (2020) — cispi.org
  2. ASTM International, "ASTM C1277-20, shielded couplings joining hubless cast iron soil pipe and fittings" (2020) — store.astm.org
  3. Cast Iron Soil Pipe Institute, "Product Specifications" — cispi.org
  4. ASTM International, "ASTM C1460-17, shielded transition couplings for dissimilar DWV pipe above ground" (2017) — store.astm.org
  5. ASTM International, "ASTM C1173-18, flexible transition couplings for underground piping systems" (2018) — store.astm.org
  6. Charlotte Pipe and Foundry, "Pressure Dimensional Catalog (DC-PR)" warranty terms (2026) — charlottepipe.com