What is a Metric Heavy Hex Screws in Inconel 718 per ASTM A1014?

Metric Heavy Hex Screws per ASME B18.2.3.3M dimensional standard, manufactured in UNS N07718 (Inconel 718 / Alloy 718) precipitation-hardening nickel-chromium superalloy per ASTM A1014 / A1014M for high-temperature bolting service to about 705 °C (1300 °F). Tensile strength ≥185 ksi (1275 MPa), 0.2% yield ≥150 ksi (1035 MPa), hardness 331–444 HBW after solution + double-age treatment.

What heat treatment is required for Metric Heavy Hex Screws in ASTM A1014?

ASTM A1014 §5.2 mandates solution treatment at 1725–1850 °F (940–1010 °C) ±25 °F with air cool or faster, followed by precipitation aging at 1325 °F (720 °C) for 8 hours minimum, furnace cool to 1150 °F (620 °C) at 100 °F/hour, hold 8 hours, air cool. Total precipitation aging cycle minimum 18 hours. Straightening permitted only between solution and aging — never after aging.

Why use Inconel 718 for Metric Heavy Hex Screws versus stainless or low-alloy steel?

Inconel 718 (Metric Heavy Hex Screws) retains its 185 ksi tensile to 705 °C where 4140 (B7), 410SS (B6), and 304/316SS lose 60-80% of room-temperature strength. Stress-rupture rating: 23 h minimum at 1200 °F / 100 ksi per ASTM A1014. Used in gas-turbine engines, liquid-oxygen turbo-pumps, downhole H₂S service, and oxy-fuel petrochemical reactors where ASTM A193 grades cannot meet service temperature.

Metric Heavy Hex Screws Inconel 718

ASME B18.2.3.3M Metric Heavy Hex Screws – Dimensions, Specifications & Standards

Metric Heavy Hex Screws for Heavy Industrial & Structural Service.

ASME B18.2.3.3M Metric Heavy Hex Screws are metric-series fasteners with a wider and taller head profile compared to standard metric hex cap screws, providing greater bearing area and superior load distribution in heavy structural, pressure vessel, and flange bolting. The standard defines metric dimensions for head height, width across flats, body diameter, thread pitch, thread length, and tolerances for global supply chain interchangeability. In high-performance applications, these screws are manufactured per ASTM A1014/A1014M for UNS N07718 (Inconel 718), offering high tensile strength, fatigue life, and corrosion resistance. Also available in ASTM A193 for high-temperature bolting and ASTM A320 for cryogenic service. Engineers must reference both B18.2.3.3M for dimensions and the appropriate ASTM specification for material properties.

ASME B18.2.3.3M Metric Heavy Hex Screws (mm)

Nominal Dia., D , and Thread Pitch	Body Diameter.,D _s	Width Across Flats,S	Width Across Corners, E	Head Height, K	Wrenching Height, K ₁	Washer Face Thickness,C	Washer FaceDia.,D _w
M12 × 1.75	12	11.73	21	20.67	24.25	23.35	7.76	7.24	5.2	0.6	0.3	19.6
M14 × 2	14	13.73	24	23.67	27.71	26.75	9.09	8.51	6.2	0.6	0.3	22.5
M16 × 2	16	15.73	27	26.67	31.18	30.14	10.32	9.68	7	0.8	0.4	25.3
M20 × 2.5	20	19.67	34	33	39.26	37.29	12.88	12.12	8.8	0.8	0.4	31.4
M24 × 3	24	23.67	41	40	47.34	45.2	15.44	14.56	10.5	0.8	0.4	38
M30 × 3.5	30	29.67	50	49	57.74	55.37	19.48	17.92	13.1	0.8	0.4	46.6
M36 × 4	36	35.61	60	58.8	69.28	66.44	23.38	21.72	15.8	0.8	0.4	55.9
All dimensions are in millimeters. Basic thread lengths, B, are the same as given in . Transition thread length, X, includes the length of incomplete threads and tolerances on grip gaging length and body length. It is intended for calculation purposes. For additional manufacturing and acceptance specifications, reference should be made to the Standard.

Nominal Dia., D , and Thread Pitch

Body Diameter.,D _s

Width Across Flats,S

Width Across Corners, E

Head Height, K

Wrenching Height, K ₁

Washer Face Thickness,C

Washer FaceDia.,D _w

Max

Min

Max

Min

Max

Min

Max

Min

Max

Min

M12 × 1.75

11.73

20.67

24.25

23.35

7.76

7.24

5.2

0.6

0.3

19.6

M14 × 2

13.73

23.67

27.71

26.75

9.09

8.51

6.2

0.6

0.3

22.5

M16 × 2

15.73

26.67

31.18

30.14

10.32

9.68

0.8

0.4

25.3

M20 × 2.5

19.67

39.26

37.29

12.88

12.12

8.8

0.8

0.4

31.4

M24 × 3

23.67

47.34

45.2

15.44

14.56

10.5

0.8

0.4

M30 × 3.5

29.67

57.74

55.37

19.48

17.92

13.1

0.8

0.4

46.6

M36 × 4

35.61

58.8

69.28

66.44

23.38

21.72

15.8

0.8

0.4

55.9

All dimensions are in millimeters.
Basic thread lengths, B, are the same as given in .
Transition thread length, X, includes the length of incomplete threads and tolerances on grip gaging
length and body length. It is intended for calculation purposes.
For additional manufacturing and acceptance specifications, reference should be made to the Standard.

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Certifications

ISO 9001 - 2015 Certified
PED 2014/68/EC
NACE MR0175/ISO 15156-2
NORSOK M-650
DFAR
MERKBLATT AD 2000 W2/W7/W10

ASME B18.2.3.3M Metric Heavy Hex Screws – Dimensions, Specifications & Standards

ASME B18.2.3.3M Metric Heavy Hex Screws (mm)

Related Specifications

Surface Treatments

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