Fastener names 2

[CamJPete]

I thought I understood this, but now I'm slight confused. It seems there are several names for cap screws and I'm trying to figure it out.

A cylindrical socket head cap screw can be called a socket head cap screw. (Not to mention hex-socket cap head screw.) I thought the cap meant that is was cylindrical...but then I saw that countersunk head is called a flat socket cap head screw. So, is a socket head cap screw implied that is cylindrical, unless there is flat in front?

Also, is flat head the preferred name to countersunk screws? Are countersunk and counterbore more reserved for hole types? (I never hear a cylindrical head referred to as a counterbore screw.)

To break it down
Cylindrical or flat refers to head depth shape
Socket refers to the drive, and is often implied to be hex
Cap refers to...the fact that it has a head? Doesn't the word head already tell us that?

Thanks for your help. I like to get the terminology correct.

 

[Ron247]

I think "cap screw" just means it goes into a threaded hole rather than a nut. They then add all the "head" configurations. Socket head cap screw, button head cap screw etc.

 

[BridgeSmith]

AFrom the way I've seen them described (which could be completely wrong), "cap screw" is used for hex head, flat, and cylindrical types; holes matching the shape of flat heads are countersunk and holes matching socket heads are counterbored, and "socket" refers to the head having a recess for a hex or other type of drive 'bit'.

The distinction between a cap screw and a bolt is what has always been the mystery to me. Maybe someone can shed some light on that as well?

 

[BridgeSmith]

Looks Like Ron247 may have answered my question while I was still writing it.

 

[Andries]

To add to Ron247s reply, screws are usually threaded the full length; bolts are partially threaded with un-threaded shanks between the threads and the head.

Andries

 

[klaus.]

unfortunately the names are different in different fields (mechanical or structural) and of course different counties
The name 'bolt' can have different meanings...

 

[AidanMc]

The screw vs. bolt thing has always bothered me because I feel like it should be more clear than it is, but that's what we get over years of use.

The last time I looked into a definition for them, what I found said that a screw threads into another part whereas a bolt goes through something and is held with a nut. So the same part can be a screw or bolt depending on the application, which seems like a pretty janky way of defining something to me. So I've given up worrying about it.

 

[BridgeSmith]

According to the Fastenal catalog one of my coworkers has, a Hex Cap Screw has a washer face on the bearing surface of the head, and "maintains a closer body tolerance", whatever that means. The Hex Bolt, in addition to those 2 differences, "does not have a machined point". Again, not sure what that means, exactly.

Presumably, that means a cap screw is intended for use without a washer under the head, while a bolt is?

 

[SwinnyGG]

"maintains a closer body tolerance", whatever that means.

Cap screws are different than bolt per ASME standards. You can read it all in B18.2.1.

They actually do have different tolerance classes and some changes in machined features (such as chamfered ends)

 

[BridgeSmith]

Thanks, jgKRI. I don't think I have access to the ASME standards with our subscriptions through IHS (just AASHTO and ASTM), but I think I understand what you're saying.

 

[drawoh]

I thought I understood this, but now I'm slight confused. It seems there are several names for cap screws and I'm trying to figure it out.

...

That barn ran away from the horse a long time ago. If you need to be clear, you need a part number or a picture. Here was a fun discussion in forum1103...

thread1103-224665

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JHG