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Hex Bolts vs. Hex Cap Screws
What are the differences between a hex cap screw and a hex bolt?
These terms are often incorrectly used interchangeably. The variations between these fasteners are fairly significant both from a manufacturing perspective and application standpoint. Generally speaking, hex cap screws are used in precise applications like an OEM setting where tight tolerances are required. Hex bolts are often specified when the mechanical properties are more important than dimensional tolerances, like the construction industry. For example, SAE J429 Grade 2 is typically provided as a hex cap screw, whereas ASTM A307-A is a common hex bolt specification.
Below is an overview of some of the specifics these fasteners are required to meet.
Hex cap screws
- Flat washer facing under the head that meet specific tolerances as described under ASME B18.2.1-1996.
- They will usually be manufactured by a cold-heading process (large runs of standard sizes) or turned CNC operation.
- A radius under the head at the shank.
- Body diameter of plus nothing, minus .011″ for an 1-1/4″ diameter fastener.
- Some common fastener specifications unless otherwise specified: ASTM A449 and SAE J429 Grade 2, 5, and 8.
- A die seam across the bearing surface is permissible.
- The typical bolt is manufactured by hot-forging process.
- Allows a reduced body diameter to be not less than the minimum pitch diameter of the thread.
- Some common fastener specifications unless otherwise specified: ASTM A307-A, A354, and F1554.
This list is not inclusive, but represents some of the differences between these two designations. There is flexibility to use other materials, grades, and bolt standards as agreed by manufacturer and purchaser. So, be cautious when ordering bolts that you make sure to be clear what type your project requires.
Posted by Greg Lindsay
Phone: (800) 599-0565 Email: greg@portlandbolt.com
View other posts by Greg Lindsay
@Muttu – We do not have any engineers of staff and are not able to make any recommendations regarding which type of fastener is better suited for a specific application.
January 8, 2013 at 11:03 amwhy are using Stud bolt, if use instead of stud bolt hex head bolt there coming any problem pls. tell me……sir.
we are using Butterfly valve to flange connection insted of Stud bolt hex. Bolt.
January 8, 2013 at 4:39 amASTM A193 covers material used in the manufacture of studs, hex bolts, bent bolts, etc; all for use in high temperature or high pressure applications (i.e. petrochemical). So there are a variety of fastener configurations that can all be certified to A193, studs and hex bolts included.
December 6, 2012 at 9:04 amI received a requirement for Bolts and the user specified the standar ASTM A193 and A194 for nuts. I got the material, but now he says that what he needs is Hex Bolts, so i think he is confused, because i know that ASTM A193 just cover Studs for intended use in oil and petrochemical industry. Could you confirm if i am right or no.
December 6, 2012 at 8:55 amThanks for you repply.
@Jeff – Yes, A193 B7 hex bolts are typically available, although it may depend on the diameter and length you need. We’d be happy to look and quote you if you’d like to contact us with the details.
October 12, 2012 at 1:08 pmAre hex bolts typically supplied in material spec A193 B7? I have a valve drawing that calls for this spec and it is described as “TRIPLEX STL.”
October 12, 2012 at 10:39 amOur normal encounter with this material spec is a threaded stud or rod.
THANK YOU!
@Bob Hinzman – A193 was written as both a material and fastener standard to cover materials used in high temperature and high pressure applications. F593 was written as a general purpose, mass produced fastener standard. F593 fasteners are typically cold formed (A193 not necessarily so), which results in higher mechanical properties. AISI 304 stainless is a stainless alloy with a specific chemical analysis, whereas 18-8 refers to the family of stainlesses that 304 is a part of. AISI 302,303,304,305,309 and others all fall into the 18-8 family. Many times the terms 18-8 and 304 are used interchangeably, however that is not necessarily correct.
June 15, 2012 at 8:22 amWouod you be able to clairify the relationship between ASTM F593D and ASTM 193. I belive they are both standards for stainless steel hex bolts and 304 and 316 stainless steel are available under both standards, but F593D bolts are 20% stronger?? Also, I’ve been told 18-8 and 304 stainless steel are the same. If they are, why are there two grades?
June 14, 2012 at 10:08 amThank you