What spec says 90 degrees for metric flathead fasteners?

[metootoo]

Every time I order a metric flathead socket cap screw it has a 90 degree head. Every time I order an english flathead socket cap screw it has a 82 degree head.

Our data entry clerk asked me which degree I wanted when I asked her to put in a 1/4-20x7/8 FHSC into the system. I said if it is english, it's always 82 and metric, always 90. She said, "no it's not."

my questions are?
1) What governs this angle (ASME, etc)?
2) Is this true for only flathead "cap" screws?
3) What does "cap screw" mean?

 

[Timelord]

metootoo,

English flat head screws come in both 82 and 90 degrees. If I don't specify, I get 82 deg. I must specify if I want 90 deg. Don't know about metric. To answer your actual questions:
1) I believe it is governed by ASTM A574.
2) No, I have bought oval head screws that were 82 deg under the head, don't know if they make 90 deg oval heads.
3) No idea where the name cap screw came from.


Timelord

 

[eromlignod]

As far as I know, 90 deg. is always metric. ANSI machine screws can be either 82 or 100 deg. ANSI capscrews are only 82. 82 is by far the dominant head and what you'll find at the hardware store.

The 100-degree head is ostensibly used in thin materials where the 82-deg. head would be too thick, though an undercut head would work as well. I have also heard that the 100 supposedly distributes the load a little more for soft materials, but I'm a little skeptical about how 9 degrees on a side is going to make a big difference, especially since the head and shank diameters are the same.

Don
Kansas City

 

[metootoo]

When I purchase a flathead "cap" screw online or from a catalog, I have never seen anything other than 82 degrees and never anything other than hex socket or torx socket. I've seen 100 degrees, but "cap" was not in the description. From observation a cap screw is a branch of machine screw, but I still don't know what defines "cap." I do however doubt that is the the "American" society of anything, as I don't believe those cover metric. DIN covers metric and MIL covers metric. I believe MIL uses other standards and narrows them down. Don't take my word on that...it's just a feeling.

 

[eromlignod]

ANSI has had standards for metric fasteners for years. We use both systems in the United States. Just because we don't eschew the other system doesn't mean we don't freely use it all the time.

Don
Kansas City

 

[tygerdawg]

Check Machinery's Handbook, it will provide the standards and diagrams for fastener geometry.

TygerDawg
Blue Technik LLC
Advanced Robotics & Automation Engineering

http://www.bluetechnik.com

 

[KENAT]

As others pointed our Metric are I believe always 90. Each country may have its own spec that says this. If you're lucky they are all based on an ISO although a lot, at least in the UK, were actually to a DIN. Take a look in machineries.

From

http://webstore.ansi.org/RecordDetail.aspx?sku=ISO 2009:1994

ISO 2009:1994
Slotted countersunk flat head screws (common head style) - Product grade A

Specifies the characteristics of slotted countersunk flat head screws of product grade A and with threads from M1,6 to M10 inclusive. If, in special cases, specifications other than those listed here are required, they should be selected from existing International Standards, e.g. ISO 261, ISO 888, ISO 898-1, ISO 965-2 and ISO 3506.

UN screws are 82 or 100 as far as I know. Machineries may tell you the standard.

KENAT, probably the least qualified checker you'll ever meet...

 

[looslib]

ASME B18.3 and ASME B18.6


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli