MF FASTENER INDUSTRIES LLC Manufacturer of anchor bolts, studs & plate washers · Importer & stockist of fasteners

Technical datasheet ASTM A194 / A194M — Nuts for high-pressure and high-temperature service

Reference only — for design, verification or contractual purposes refer to the current issue of the original standard. MF Fastener Industries LLC · sales@mfindllc.com · +971 6 767 2469 · mfindllc.com

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Dimensional datasheet

ASTM A194 heavy hex nut

Heavy hexagon nuts for bolting under high pressure, high temperature, or both. Grade 2H is the standard partner to A193 B7 and covers most process piping. Other grades exist for sour, low-temperature and stainless service.

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d nominal thread diameters width across flatse width across cornersm nut height

Dimensions

inches

Heavy hex dimensions to ASME B18.2.2. UNC to 1 inch, 8 UN above. A heavy hex nut is wider across flats and thicker than a standard hex nut and is not interchangeable.

Size	Thread	s — across flats	Spanner size	m — nut height
1/2"	13 UNC	7/8"	7/8"	31/64"
5/8"	11 UNC	1-1/16"	1-1/16"	39/64"
3/4"	10 UNC	1-1/4"	1-1/4"	47/64"
7/8"	9 UNC	1-7/16"	1-7/16"	55/64"
1"	8 UN	1-5/8"	1-5/8"	63/64"
1-1/8"	8 UN	1-13/16"	1-13/16"	1-7/64"
1-1/4"	8 UN	2"	2"	1-7/32"
1-1/2"	8 UN	2-3/8"	2-3/8"	1-15/32"
1-3/4"	8 UN	2-3/4"	2-3/4"	1-23/32"
2"	8 UN	3-1/8"	3-1/8"	1-31/32"

The grade is the specification, not the shape

Every A194 nut is a heavy hex. What distinguishes the grades is material and heat treatment: 2H is quenched and tempered carbon steel; 2HM is tempered softer for sour service; 4 and 7 are alloy for low temperature; 8 and 8M are stainless.

Ordering 'A194 nuts' without a grade tells a supplier almost nothing.

2H and 2HM are not interchangeable

2H — 248 to 327 HBW, the standard partner to B7. 2HM — 159 to 237 HBW maximum, tempered softer to satisfy NACE MR0175 for sour service.

A 2H nut in a sour-service joint fails the specification even though it is stronger. Hardness is the controlled property, and lower is the requirement.

Grades and pairing

A194 / A193 / A320

Grade	Material	Hardness	Pair with	Service
2H	Carbon steel, Q&T	248 – 327 HBW	A193 B7, B16	High temperature
2HM	Carbon steel, Q&T	159 – 237 HBW	A193 B7M	Sour service, NACE
4	Alloy steel, Q&T	248 – 327 HBW	A320 L7, L7M	Low temperature
7	Alloy steel, Q&T	248 – 327 HBW	A320 L7, L43	Low temperature, impact tested
8	Type 304 stainless	126 – 300 HBW	A193 B8	Corrosive, high temperature
8M	Type 316 stainless	126 – 300 HBW	A193 B8M	Chloride service

Grade is stamped on the nut face. An unmarked nut in a pressure joint cannot be verified and should be rejected.

Metric — A194M

ASTM A194M

Size	Pitch	s — across flats	Spanner size	m — nut height
M16	2.00	27 mm	27 mm	17.1 mm
M20	2.50	34 mm	34 mm	20.7 mm
M24	3.00	41 mm	41 mm	24.2 mm
M27	3.00	46 mm	46 mm	27.6 mm
M30	3.50	50 mm	50 mm	30.7 mm
M36	4.00	60 mm	60 mm	36.6 mm

Metric grades carry an M suffix, as in Grade 2HM — do not confuse that with the sour-service 2HM in imperial, which is a hardness limit, not a unit.

At a glance

Standard	ASTM A194 · A194M
Form	Heavy hexagon, chamfered
Common grade	2H
Thread	UNC to 1 in · 8 UN above
For A193 B7	Grade 2H
For A193 B7M	Grade 2HM
For A320 L7	Grade 4 or 7
For A193 B8 / B8M	Grade 8 · 8M
Structural equivalent	ASTM A563 — not a substitute

Supply

Imported and held in stock, sourced from established mills and supplied from our warehouse in Umm Al Quwain.

Supplied with our own stud bolts as a matched set where the joint calls for it.

Finish

Plain	Black, oiled — the normal supply
PTFE / Xylan	Matched to coated studs
Hot-dip galvanized	Oversize tapped, where permitted
Certification	Mill certificate, EN 10204 3.1 as standard

Testing

Dimensional and thread inspection is carried out in our own plant on calibrated instruments. Tensile, hardness and chemical testing is carried out by independent UAE-accredited laboratories.

Reference only

This datasheet is published for reference. Dimensions and property values are reproduced in good faith from published standards, but for design, verification or contractual purposes always refer to the current issue of the original standard.

If a figure here conflicts with the standard, the standard governs.

Need a quotation?

Send the size, grade, finish and quantity, and the stud grade you are pairing with so we can confirm the nut suits the service.