ASME B16.11 Hex Head Bushing is a forged threaded fitting with male (external) NPT threads on the larger end and female (internal) NPT threads on the smaller end. The hex section at the top provides a flat surface for a wrench. It reduces pipe size within a threaded assembly without requiring additional fittings downstream. Contact us to get free quote and sample!
NPT vs BSPT: which thread type to specify
This is where a lot of cross-border orders get complicated. ASME B16.11 defines dimensions for NPT threads per ASME B1.20.1. The standard does not cover BSPT (BS EN 10226) or BSPP threads. Yet a large portion of instrumentation and process equipment used in the Middle East and Europe has BSP-threaded ports.
- NPT threads - 60° thread angle, taper 1:16. Standard for American-designed equipment and most North American-specification EPC projects. Applies to: Saudi Aramco, ADNOC, QatarEnergy, US spec EPC.
- BSPT threads - 55° thread angle (Whitworth form), taper 1:16. Common on European-origin instrumentation and older GCC equipment built to British specifications. Not interchangeable with NPT - forced engagement causes galling and immediate leak paths. Applies to: European instrumentation, British-spec installations, Shell DEP projects.
Material grades
| Grade | Standard | Typical use case | Notes |
|---|---|---|---|
| A182 F304/F304L | ASTM A182 | Dilute acids, food-grade, mild chloride | L grade for weld-adjacent fittings to avoid sensitisation. |
| A182 F316/F316L | ASTM A182 | Seawater cooling, produced water, chloride streams | Mo addition (2–3%) is what separates 316 from 304. L grade is standard for offshore GCC. |
| A182 F51 (S31803) | ASTM A182 | High-chloride produced water, CO2 injection | Duplex yields roughly double the strength of 316L. Check PREN >35 for Gulf seawater. |
| A182 F60/F65 (S32750) | ASTM A182 | Aggressive produced water, offshore umbilicals | Super duplex, PREN typically >40. Price premium 4–6x over 316L is normal. |
|
Nominal size |
Length |
Square height |
Width flats |
Head diameter |
Length |
Hex height |
Hex height |
Hex height |
|
|
DN |
NPS |
Amin |
Bmin |
Cmin |
Emin |
Dmin |
Hmin |
Gmin |
Fmin |
|
6 |
1/8 |
10 |
6 |
7 |
10 |
35 |
6 |
一 |
11 |
|
8 |
1/4 |
11 |
6 |
10 |
14 |
41 |
6 |
3 |
16 |
|
10 |
3/8 |
13 |
8 |
11 |
18 |
41 |
8 |
4 |
18 |
|
15 |
1/2 |
14 |
10 |
14 |
21 |
44 |
8 |
5 |
22 |
|
20 |
3/4 |
16 |
11 |
16 |
27 |
44 |
10 |
6 |
27 |
|
25 |
1 |
19 |
13 |
21 |
33 |
51 |
10 |
6 |
36 |
|
32 |
11/4 |
21 |
14 |
24 |
43 |
51 |
14 |
7 |
46 |
|
40 |
11/2 |
21 |
16 |
28 |
48 |
51 |
16 |
8 |
50 |
|
50 |
2 |
22 |
18 |
32 |
60 |
64 |
18 |
9 |
65 |
|
65 |
21/2 |
27 |
19 |
36 |
73 |
70 |
19 |
10 |
75 |
|
80 |
3 |
28 |
21 |
41 |
89 |
70 |
21 |
10 |
90 |
|
100 |
4 |
32 |
25 |
65 |
114 |
76 |
25 |
13 |
115 |
FAQ
Q: What is the difference between Class 3000 and Class 6000?
Class 3000 is rated for use with Sch 80 pipe; Class 6000 for Sch 160. The 6000# fitting is physically larger in the same NPS. Class 6000 is typically used for high-pressure instrument take-offs, injection quills, and wellhead-adjacent connections.
Q: Can I use a hex head bushing for a two-size reduction (e.g., 2" to 1/2")?
Not in a single fitting. ASME B16.11 only covers single-step reductions. For two-step reductions, use a reducing coupling plus a second bushing, or a custom adapter that needs separate qualification.
Q: What does NPS mean in the size designation?
NPS is a dimensionless designator, not the actual pipe OD. For a hex bushing, the NPS refers to the male (larger) end thread. "NPS 1 × NPS 1/2" = 1-inch male NPT thread outside, 1/2-inch female NPT thread inside.
Q: How are ASME B16.11 hex head bushings marked?
Minimum markings: manufacturer name/trademark, material grade, pressure class, NPS. On small-bore fittings (1/2" and below), bag/box marking is acceptable. Heat number on the fitting must match the MTC. Illegible or absent heat numbers on certified projects are a valid NCR trigger.
Q: Is there a socket-weld version?
No. The hex bushing geometry is threaded-only. The socket-weld reducing insert is the closest welded alternative.
Q: What tolerances apply to the F dimension (hex across flats)?
-0.00 / +1.59 mm for hex sizes up to 50.8 mm; -0.00 / +3.18 mm above that. Oversized is allowed, undersized is not.
