Socket head cap screws vs Hex head fasteners

[Hakeem]

I was wiring a soon-to-be machine shop today and noticed the use of large socket head cap screws for fastening the cranes to the steel posts.



All 8 cranes were fastened to the post with SHCS.

Is there a reason to use these over the more-commonly seen hex head fasteners? Or was this likely a case of using whatever is rolling around in the back of the truck?

 

[garfunkle24]

Probably just because you can run those in with an impact without unpinning the crane arm. Doesn't look like you could get a socket on a hex bolt right there. I see no other reason.

 

[Hakeem]

Probably just because you can run those in with an impact without unpinning the crane arm. Doesn't look like you could get a socket on a hex bolt right there. I see no other reason.

Of course, that would make perfect sense. I believe you’re right about the limited access … I’ll double check tomorrow to verify.

That was easy

 

[Firebrick43]

Most CNC machines are put together nearly exclusively with shcs. Therefore in the machine shops that I have worked in as an mech on them, the fastener cribs bolt bins were very well stocked with shcs and very light on hex head screws.

 

[Signing off]

The shcs often are 12.9 grade, stronger than grade 8 bolts which are common but weaker.

 

[MWEric]

We put together large aerospace machinery (waterjets, friction stir welders, etc.) engineering specs out SHCS for basically everything.

 

[Rusted Nut]

SHCS have a larger head diameter, stronger than hex head for same shank size.

 

[nadogail]

Ham Handed "Handy Men" don't usually have large Hex Keys.

 

[danielbuck]

Ham Handed "Handy Men" don't usually have large Hex Keys.

I resemble that remark, sir.

 

[NORTON'S SHOP]

Probably used what was on the shelf. I've worked in a machine shop environment for almost forty-five years. The SHCS selection is/was usually ten times larger than the hex head fasteners.

 

[bwringer]

Probably just because you can run those in with an impact without unpinning the crane arm. Doesn't look like you could get a socket on a hex bolt right there. I see no other reason.

The shcs often are 12.9 grade, stronger than grade 8 bolts which are common but weaker.

Yup and yup.

I've found, at least with the metric motorcycle stuff I generally monkey with, that the only fasteners easily available in the highest grade, 12.9, are SHCS. Hex head fasteners often top out at 10.9.

For example, the Kawasaki KLR650 has a few rather famous weak points in the frame that are solved by upgrading the fasteners to 12.9 SHCS.

Hex heads in 12.9 do exist, but there's a much greater variety available in SHCS. In 8mm at McMaster-Carr, there are only 14 variations in 12.9 hex head screws available, and 117 in SHCS.

The fact that they also keep morons from using an adjustable wrench to mess with them could also be seen as a minor bonus.

 

[sz0k30]

Worked in the auto industry (primarily large trucks - semi's) for a lot of years. Almost never used allen head bolts. They were used a lot in tooling, but those were all grade 8. Till this post never heard of grade 12.9. Almost sounds more metric than SAE.

 

[Fixr]

Worked in the auto industry (primarily large trucks - semi's) for a lot of years. Almost never used allen head bolts. They were used a lot in tooling, but those were all grade 8. Till this post never heard of grade 12.9. Almost sounds more metric than SAE.

That's only because it is metric.

 

[Riverrat]

One advantage is that the head size is smaller. Something that is overlooked is the shank length. Make sure that the threads regardless of the fastener are not in shear. I have seen this too many times and the threads act like a low speed end mill and egg the hole and eventually there is a failure especially in race car applications. I look at my Ford truck and they obviously didn't care and I can already see the results.

 

[stockerwithalocker]

A socket head cap screw (shcs) is stronger and has a tighter shank tolerance than typical bolts. A grade 8 bolt is 150 ksi ultimate strength. A shcs is 170-180 ksi depending on size, so a good amount stronger. The shank of a shcs is typically truer to size, where the grade 8 is a bit undersize. In my mind, it’s a cheaper option to a NAS bolt if you don't need a hex head and certs.

 

[Riverrat]

A socket head cap screw (shcs) is stronger and has a tighter shank tolerance than typical bolts. A grade 8 bolt is 150 ksi ultimate strength. A shcs is 170-180 ksi depending on size, so a good amount stronger. The shank of a shcs is typically truer to size, where the grade 8 is a bit undersize. In my mind, it’s a cheaper option to a NAS bolt if you don't need a hex head and certs.

I agree with you and when you think about it it's a no brainer. When I was a missile mechanic we had to have holes we drilled checked with go/no-go gages to make sure they met the tolerance of the fastener. This is beyond what the average fabricator would do but it should still be a consideration. A little off topic but still important. Deburr the holes you drill. Having a counter sink in a cordless drill is a good thing to have on hand. Just my two cents.

 

[rslaback]

I find that when I reassembly parts after restoration I tend toward SHCS or BHCS because they don't mar the paint outside of the finished footprint of the fastener like a hex does.

 

[rattle_snake]

I like the look/style of SS SHCS, or socket head anything. A fastener ***** I guess.

But I have found they **** to work on and ended up going back to philips and hex in a lot of places to minimize the number of tools needed to perform a simple fix. Different SH fasteners use different size keys even with same thread (1/4-20 for example).

 

[RoninB4]

To set the head below a surface the C'bore for a SHCS is much smaller than what's required for a HHCS + the additional room for the socket to remove it. This is seen more often on industrial machinery than consumer goods.