What is the difference between F594 and A194 nuts?

For this FAQ, we are focusing on the 304/316 alloys and their common, default strength conditions. Within both F594 and A194, there are many less common, exotic grades and multiple strength conditions. Exploring all possible permutations of all grades would be unnecessarily complicated. For more details, the actual ASTM standards can be purchased from ASTM, or specific questions can be asked of myself or any of our inside salespeople.

The differences between the two standards are primarily mechanical, dimensional, and application-based.
A194 nuts are intended for high-temperature applications, although they are certainly used in many, non-high-temperature applications as well.
F594 nuts are intended for general purpose applications.

We can compare the nuts using three metrics; chemistry, mechanical properties, and dimensions.

Chemically, the nuts are identical. F594 group 1 nuts are made from 304 stainless, as are A194 gr.8 nuts.
F594 group 2 nuts are made from 316 stainless, as are A194 gr.8M nuts.

A194 gr.8 A194 gr.8M F594 Alloy Group 1 F594 Alloy Group 2
AISI 304 AISI 316 AISI 304 AISI 316

Mechanically, there are small differences between the standards.
F594 condition CW – minimum proof load 100ksi up to 5/8” diameter, 85ksi diameters ¾” and up.
A194 – minimum proof load 80ksi for all diameters

Grade Proof load, lbf
A194 gr. 8, all sizes 80,000
A194 gr.8M, all sizes 80,000
F594 CW, sizes up to 5/8” 100,000
F594 CW, sizes above 5/8” 85,000

Dimensionally, the two nuts are different.
A194 nuts are made to heavy hex dimensions, whereas F594 nuts are made with standard hex dimensions. Heavy hex nuts are 1/8” thicker across the flats regardless of diameter, and are also slightly taller, although that dimension varies by diameter. You can see the size comparisons here:
Standard Hex Nuts
Heavy Hex Nuts
Specials can, of course, be made to alternate dimensions, but the default, off the shelf dimensions, are as above.

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