style 31 line cap
style 31 line cap

Dresser Style 31 | Line Cap | Cast Iron Pipe

Nominal Size: 2 in
Outside Diameter: 2.5 in
Middle Ring Length: 5 in

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$476.48
SKU: 0031-0002-204
Weight : 12.0 lb
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Description
Dresser Bolted Line Cap

Style 31 Line Cap
Cast Iron Pipe

Bolted slip-on end cap for plain-end cast iron pipe in nominal sizes 2 in through 24 in. Sized to cast-iron pipe ODs (Class A through D variations) for testing dead-ends, capping retired services, or terminating CI pipe stubs — no welding, threading, or pipe preparation required.

Sizes 2 in – 24 in
Multiple CI Class Options
150 PSI MAOP All Sizes
1 in NPT Vent Standard
Built from Style 38 Parts
Need to cap steel pipe instead? Steel pipe has a smaller OD than cast iron pipe at the same nominal size (e.g., 6 in steel = 6.625 OD, 6 in CI = 6.900 or 7.100 OD). The Style 31 Line Cap for Steel Pipe is sized accordingly — verify your pipe material before ordering.
View Steel Pipe Version →
Overview

The Dresser Style 31 Line Cap for Cast Iron Pipe is a purpose-built, gasketed end cap used to close off cast iron pipelines during construction and pressure testing, and to permanently cap dead-end CI stubs or retired services. Constructed from standard Style 38 coupling components with a convex dished steel head welded into one end of the middle ring, the Style 31 eliminates the need for blind flanges, threaded plugs, or field-fabricated end closures.

Cast iron pipe varies in actual outside diameter across pipe classes (A, B, C, D) and manufacturing standards, so most nominal sizes are available in multiple OD variants — for example, 6 in CI is offered at both 6.900 and 7.100 OD, and 8 in CI at both 9.050 and 9.300 OD. Verify your cast iron pipe’s actual OD class before ordering. Rated 150 PSI MAOP in all sizes; higher pressures available per application.

Key Features
Tool-Only Installation
Gasketed slip-on design installs on plain-end pipe with standard coupling bolts — no threading, beveling, welding, or special tools.
Convex Dished Head
Steel convex dish welded into one end of the middle ring provides structural resistance to internal pressure loading across all sizes.
Built from Style 38 Parts
Same followers, gaskets, and bolt design as the proven Dresser Style 38 coupling. One follower is factory-welded to the cap; only one field-installed follower and one gasket required.
1 in NPT Vent Standard
Off-center vent and plug allows air purging and pressure equalization during filling and hydrostatic testing (2 in & 3 in sizes: vent in center of head). Caps without vents available on request.
150 PSI MAOP All Sizes
Rated 150 PSI Maximum Allowable Operating Pressure across the full size range. Higher pressures available per application — consult factory.
Armored Gasket
Grade 27 BUNA-S armored gasket with pinned-armor reinforcement for blowout and extrusion resistance under service pressure.
Fusion-Bonded Grey Epoxy
Factory-applied coating for corrosion resistance in buried and exposed service. Dresser RED-D Shopcoat finish available as an option — consult factory.
Insulating Design Available
Insulating version with insulating gasket, insulating sleeve, and pipe-end separator available for cathodic protection applications. Consult inside sales for project requirements.
Materials of Construction
Followers
AISI C1012 or ASME SA36
One welded to cap; one field-installed
Middle Ring (Cap Body)
ASTM A513 / A635 / SA675 Gr.60
Steel sleeve with welded dished head
Dished Head
Convex Carbon Steel
Welded into one end of middle ring
Bolts & Nuts
AWWA C111 / ANSI A21.11
Standard coupling hardware
Gasket
Grade 27 BUNA-S Armored
One gasket per cap; pinned-armor reinforcement
Coating
Fusion-Bonded Grey Epoxy
Dresser RED-D Shopcoat optional
Vent
1 in NPT with Plug
Off-center standard (center on 2 in / 3 in)
Insulating Option
Available on Request
Insulating gasket + sleeve + pipe-end separator
Engineering References & Downloads
Style 31 Submittal PDF
Official Dresser product brochure covering Style 31 Line Caps. Includes design rationale, materials of construction, dimensional diagram, and complete spec tables for both steel and cast iron pipe applications. For engineering review and project files.
Download Submittal
Pipe OD Reference Chart
Outside-diameter cross-reference for steel, PVC, polyethylene, ductile iron, cast iron (all classes), and asbestos cement pipe — sizes 1/2 in to 60 in. Verify pipe OD before specifying cap size.
Download Pipe Chart
Sizes & Specifications — Cast Iron Pipe
Nominal Size Pipe OD (in) Middle Ring (Thick × Len, in) Bolts (No. × Diam × Len, in) Working PSI Ship Wt (lbs)
2 in 2.500 .187 × 5 3 — 5/8 × 8-1/4 150 12
3 in 3.800 .188 × 5 4 — 5/8 × 8-1/4 150 14
3 in 3.960 .203 × 5 4 — 5/8 × 8-1/4 150 18
4 in 4.800 .229 × 5 4 — 5/8 × 8-1/4 150 22
4 in 5.000 .229 × 5 4 — 5/8 × 8-1/4 150 23
6 in 6.900 1/4 × 5 6 — 5/8 × 8-1/4 150 32
6 in 7.100 1/4 × 5 6 — 5/8 × 8-1/4 150 37
8 in 9.050 1/4 × 5 6 — 5/8 × 8-1/4 150 42
8 in 9.300 1/4 × 5 6 — 5/8 × 8-1/4 150 45
10 in 11.100 3/8 × 7 8 — 5/8 × 10-3/4 150 71
10 in 11.400 3/8 × 7 8 — 5/8 × 10-3/4 150 72
12 in 13.200 3/8 × 7 8 — 5/8 × 10-3/4 150 100
12 in 13.500 3/8 × 7 8 — 5/8 × 10-3/4 150 106
14 in 15.300 3/8 × 7 10 — 5/8 × 10-3/4 150 120
14 in 15.650 3/8 × 7 10 — 5/8 × 10-3/4 150 124
16 in 17.400 3/8 × 7 10 — 5/8 × 10-3/4 150 136
16 in 17.800 3/8 × 7 10 — 5/8 × 10-3/4 150 147
18 in 19.500 3/8 × 7 12 — 5/8 × 10-3/4 150 163
18 in 19.920 3/8 × 7 12 — 5/8 × 10-3/4 150 167
20 in 21.600 3/8 × 7 12 — 5/8 × 10-3/4 150 183
20 in 22.060 3/8 × 7 14 — 5/8 × 10-3/4 150 192
24 in 25.800 3/8 × 7 15 — 5/8 × 10-3/4 150 230
24 in 26.320 3/8 × 7 15 — 5/8 × 10-3/4 150 235

Multiple OD options per nominal size correspond to different cast iron pipe classes (A, B, C, D). Cast iron pipe OD varies by class and manufacturing standard — verify your actual CI OD before ordering. See Pipe OD Reference Chart above. All Style 31 Line Caps supplied with 1 in NPT vents as standard. Higher pressures available per application.

⚠ Seal Only — Anchorage or Blocking Required Under Pressure
Style 31 Line Caps provide a pressure seal only — they do NOT provide pipe restraint. Line Caps must NOT be used under pressure WITHOUT ANCHORAGE OR BLOCKING sufficient to withstand the entire longitudinal thrust due to internal pressure. Use thrust blocks, anchor straps, or restraint harnesses appropriate for your working pressure and pipe size before pressurizing the line. Failure to anchor the cap could result in cap blow-off, escaping line content, property damage, serious injury, or death.
Don’t Know Your Cast Iron Pipe’s OD?
Cast iron pipe outside diameter varies by class and manufacturing era. AWWA Pit Cast Classes A through D, Ductile Iron Pipe, and Class 100 – 250 Centrifugally Cast all use slightly different ODs at the same nominal size. The Pipe OD Reference Chart in the Downloads section above lists all common cast iron OD ranges. If you can’t identify your pipe class, measure the actual OD with a pi tape or calipers before ordering — the wrong OD cap will not seal.
Consult Inside Sales For
Caps without vents, lock-pin caps for thrust restraint, insulating versions for cathodic protection, higher pressure ratings, sizes above 24 in, alternative gasket compounds, American Iron & Steel (AIS) or BABAA certification, all-stainless construction, or Dresser RED-D Shopcoat finish.
Ready to Order?
Confirm pipe OD, vent configuration, and any cathodic protection requirements before placing your order.
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Submittal

Style 31 Line Cap Submittal

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