April '21 Update: HART announces expanded manufacturing capacity for Carbon Steel Industrial Unions! Class 3000 and 6000.

Copper Sweat Unions

Hart Copper Sweat Tube Union

Fail Safe Leakproof Reliability

At any pressure, HART O-Rings actually strengthen the seal rather than loosen it.

VViton® Florocarbon A (FKM-A)
EEthylene Propylene (EPDM)
ESHigh-Temp Steam EPDM [up to 550*F max] (EPDM E0962)
TTeflon® Tetrafluoroethylene (PTFE)
BNitrile / Buna N (NBR)
NNeoprene® Polycloroprene (CR)
KKalrez® 4079 Perfluoroelastomer (FFKM)
HNHydrogenated Nitrile (HNBR)
EPNSF-61 Approved EPDM (Ethylene Propylene)
GMetallic Graphite Spiral Wound Seal
INo O-Ring (Integral Seat "Ball to Cone")
Teflon®, Viton®, Kalrez® are
Registered Trademarks from DuPont


The O-ring is fitted into a machined groove between the two halves of the union. When the halves are drawn together the O-ring compresses to an ovalized cross-section, forming a positive, resilient seal which serves to block the fluid, thus sealing even at low or no pressure.

Under Load

As pressure is increased the O-ring is forced to flow and is "squeezed" into the downstream side causing the O-ring to conform to the shape of the end, blocking the groove gap. The more the system pressure increases, the more effective the seal.

Straight-Away Breakout

The flat faced construction allows for slipping the component in and out without disturbing the surrounding tube or pipe sections. Pipe alignment is much easier with Hart Unions since it is unnecessary to spring the line during make-up or disassembly.

Specialty Orders

Specialty O-Rings also available. Inquire within.


The charts below contain all the information necessary to place an order. Use the appropriate codes in the manner shown below.

Example: a Class 3000 Female Threaded 1" Union with Viton O-ring and 316 Stainless Steel Ends is coded as follows:

When a size reduction or change in material is needed, simply enter the Tailpiece code and then the Threadpiece code separated by a slash as shown below.

Example: A Dielectric Class 3000 Union with a Dielectric Coated A105 Carbon Steel Tailpiece that is 3/4" Female NPT, with a 304 Stainless 1/2" Male NPT Threadpiece, Teflon O-Ring, is coded as follows:

For more information, a quote, or to order, call 1-800-769-0503 or contact us at sales@hartindustries.com

O Orifice
D Dielectric (Insulating)
H Hammer Lug


Female NPT (FNPT) Class 3000 Pipe 31 31 0  (1/8")
1  (1/4")
2  (3/8")
3  (1/2")
4  (3/4")
5  (1")
6  (1 1/4")
7  (1 1/2")
8  (2")
9  (2 1/2")
10 (3")
11 (3 1/2")
12 (4")

V Viton® Florocarbon A (FKM-A)
E Ethylene Propylene (EPDM)
ES High-Temp Steam EPDM [up to 550*F max] (EPDM E0962)
T Teflon® Tetrafluroethylene (PTFE)
N Neoprene® Polychloroprene (CR)
K Kalrez® 4079 Perfluoroelastomer (FFKM)
HN Hydrogenated Nitrile (HNBR)
EP NSF-61 Approved Ethylene Propylene (EPDM)
G Metallic Spiral Wound Graphite Seal
I No O-Ring (Integral Seat "Ball and Cone")
Teflon®, Viton®, Kalrez® are
Registered Trademarks from DuPont
Male NPT (MNPT) Class 3000 Pipe 32 32
Socket Weld (SW) Class 3000 Pipe 33 33
Socket Weld (SW) Class 3000 Tube 34 34
Butt Weld (BW) Class 3000 Pipe 35 35
Sweat Copper Tube 36 36
Female NPT (FNPT) Class 6000 Pipe 61 61
Male NPT (MNPT) Class 6000 Pipe 62 62
Socket Weld (SW) Class 6000 Pipe 63 63
Socket Weld (SW) Class 6000 Tube 64 64
Butt Weld (BW) Class 6000 Pipe 65 65
A Aluminum
B Brass 464 or 360
CS A105 Carbon Steel
304 A182F304/304L Stainless Steel
304L A182F304/304L Stainless Steel
316 A182F316/316L Stainless Steel
316L A182F316/316L Stainless Steel
A20 Alloy 20 (Carpenter Steel C20)
73 70/30 Copper Nickel
91 90/10 Copper Nickel
H Hastelloy C-276
I Inconel 600
M Monel 400
T Titanium


MNPT: Place desired MNPT Wall Thickness in parentheses. Note: S40 Standard for Class 3000 and S80 Standard for Class 6000 unless otherwise specified.
Example: 6262-5-V-304(S160)
Butt Weld Pipe: Place desired BW Wall Thickness in parentheses. Note: S40 Standard for Class 3000 and S80 Standard for Class 6000 unless otherwise specified.
Example: 3535-5-V-304(S40)
Orifice Unions: Place desired drilled orifice bore in parentheses.
Example: O-3131-5-V-304(0.250")


BSPT-F BSPT (British Standard Pipe Taper) - Female, Rc
BSPT-M BSPT (British Standard Pipe Taper) - Male, R
BW TUBE Butt Weld with Tube O.D.
MALE PIPE END Male Pipe End (unthreaded) for socket welding.
ACME Nut ACME Thread Nut for specialty applications


Call to Order: 800-769-0503

3636 Series

Copper Sweat Tube, Class 3000 Unions

HART Industrial O-Ring Unions are engineered to provide Class 3000 Service and are the most popular union in the industry for general purpose applications. The flat face design provides turbulence-free fit across seats. This design is ideal where piping requirements dictate the necessity of having a flat face seal to make and break the pipe line. All HART Unions are made in the USA!

Standard O-Ring Union Features:

  • Turbulence Free: All unions provide a turbulence-free fit across the seats
  • O-Ring Isolation: The O-Ring seal is strategically located in the thread piece face reducing O-Ring media contact and added protection against abrasives and erosion.
  • Precision Machined components: All unions are precision machined to provide high quality and fail-safe leak proof reliability.
  • Interchangeable End Connections: Threaded, socket weld, and butt-weld ends are interchangeable. This feature reduces overall costs by eliminating unnecessary nipples, bushings, couplings and inserts.
  • Material Versatility: Unions can be provided in all standard metals or combination of metals. This includes 304 Stainless, 316 Stainless, A 105 Carbon Steel, Brass, Monel 400, Hastalloy, and Titanium.
  • Excellent vibration resistance: Seals will not loosen, even under extreme pressure and pressure surges.

3D Animations


3636-1 1/4" 1.63 1.50 0.86 0.78 0.83 0.33
3636-2 3/8" 1.82 1.69 1.02 0.88 0.91 0.4
3636-3 1/2" 1.94 1.87 1.23 0.92 0.99 0.7
3636-4 3/4" 2.36 2.20 1.46 1.11 1.23 1
3636-5 1" 2.45 2.62 1.79 1.17 1.25 1.75
3636-6 1-1/4" 2.80 3.06 2.16 1.38 1.39 2.5
3636-7 1-1/2" 3.01 3.37 2.42 1.50 1.17 3.5
3636-8 2" 3.40 4.12 2.96 1.65 1.72 4.25
3636-9 2-1/2" 4.03 5.00 3.61 1.98 2.01 6
3636-10 3" 4.30 5.62 4.30 2.13 2.13 8