Socket head cap screws

The Junk Drawer is for those Off Topical discussions where we can ask questions of the community that we feel might have the ability to help out.

Moderator: Harold_V

earlgo
Posts: 1794
Joined: Sat Jan 29, 2011 11:38 am
Location: NE Ohio

Socket head cap screws

Post by earlgo »

Having been a mechanical design engineer for 50 odd years, I ran across something a couple of years ago that made me wonder. I found a #12-24 tap and die in the box of "inventory" that my dad had with the Atlas lathe. I didn't think any more of it because it was an "odd" size. Last year I found a #12-24 tap at the local Ace hardware and bought it just to see how soon it would be replaced. A replacement was there within 2 weeks.
Recently just for fun I ordered a box of #12-24 socket head cap screws from McMaster-Carr and it came in a green box marked with no name, just a phone number. The screws are stamped 'CAMCAR'. Normally McM-C screws come in a black box marked "Brighton Best" with no stamping on the screw.
Neither the Unbrako Socket Screw Selector nor the Holo-Krome Socket Screw Selector slide cards list a #12. #0,1,2,3,4,5,6,8,10 are listed but then jumps to 1/4" and larger fractional sizes.
A #12 screw is .216 diameter right between the .187 diameter #10 and the .250 diameter 1/4".
#10, #12, 1/4in
#10, #12, 1/4in
Do any of you wizards know why #12 screws are not commonly used?
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
User avatar
mklotz
Posts: 428
Joined: Thu Jan 09, 2003 11:35 am
Location: Los Angeles, CA, USA
Contact:

Re: Socket head cap screws

Post by mklotz »

Electronic racks are one place they are used...

https://www.racksolutions.com/news/data ... explained/

I believe some old woodworking equipment, e.g. planes, used that size for adjustment screws but I'm not a woodworker so take that with a grain of salt.
Regards, Marv

Home Shop Freeware
http://www.myvirtualnetwork.com/mklotz
John Hasler
Posts: 1852
Joined: Tue Dec 06, 2016 4:05 pm
Location: Elmwood, Wisconsin

Re: Socket head cap screws

Post by John Hasler »

They are common in electrical equipment.
Russ Hanscom
Posts: 1955
Joined: Wed Mar 15, 2006 11:10 pm
Location: Farmington, NM

Re: Socket head cap screws

Post by Russ Hanscom »

Probably manufacturers trying to simplify their inventory. I have a #12 tap and die, and a few other weird ones, legacies from grandfather. Hoping to keep then as curiosities only. Most are close enough to something else as to not be really needed and they are an invitation for a careless person to use the wrong size.
User avatar
Steggy
Posts: 1976
Joined: Tue Jun 28, 2011 9:19 pm
Location: JB Pritzker’s Hellhole
Contact:

Re: Socket head cap screws

Post by Steggy »

In the past, I've seen 12-24 machine screws used in some power tools—it seems to be a rarely-used size these days. I have a 12-24 gun tap and a 12-24 die in my tap-and-die set, but can't recall if I've ever used either one.

CamCar is/was a large manufacturer of socket screw products. Dunno if they're still around.

My Craftsman Handbook of Taps, Dies and Threading Accessories (published in 1968) lists 12-24 as a stock size. However, my Blue Devil slide card jumps from #10 to 1/2".
———————————————————————————————————————————————————————
Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Socket head cap screws

Post by Harold_V »

BigDumbDinosaur wrote: Sun Mar 07, 2021 6:08 pm my Blue Devil slide card jumps from #10 to 1/2".
½"? Not ¼"?

H
Wise people talk because they have something to say. Fools talk because they have to say something.
User avatar
Steggy
Posts: 1976
Joined: Tue Jun 28, 2011 9:19 pm
Location: JB Pritzker’s Hellhole
Contact:

Re: Socket head cap screws

Post by Steggy »

Harold_V wrote: Mon Mar 08, 2021 2:53 am
BigDumbDinosaur wrote: Sun Mar 07, 2021 6:08 pm my Blue Devil slide card jumps from #10 to 1/2".
½"? Not ¼"?

H
Yep! It's supposed to be 1/4. I tried to fix that after I saw my error and had already posted, but the forum software refused to let me do it. It was within a minute or two after posting, so it was a case of being timed out.
———————————————————————————————————————————————————————
Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
earlgo
Posts: 1794
Joined: Sat Jan 29, 2011 11:38 am
Location: NE Ohio

Re: Socket head cap screws

Post by earlgo »

Russ Hanscom wrote: Sun Mar 07, 2021 4:29 pm Probably manufacturers trying to simplify their inventory. (....) Most are close enough to something else as to not be really needed and they are an invitation for a careless person to use the wrong size.
Oh, that explains everything. I have often used #0, #1, #2, and #3 screws and the hardware is full of them in different sizes, and the taps and dies are there, too. OK, not so much. But strangely enough McM-C carries socket head screws down to #0000-160! good grief, I would hate to drop one in the lathe chip tray. Major dia is .021 with 160 threads per inch and head size of .035. Thread pitch would be .006. My thread wire kit didn't have wire for checking those, for sure.
Still not a useable answer as to why #12 screws are not that commonly used for other things than electronic equipment.
My next project will use them if it is relevant. More or less to tick of the next user, I guess. :D
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
User avatar
mcostello
Posts: 963
Joined: Sat Jan 04, 2003 10:45 pm
Location: Lancaster, Ohio

Re: Socket head cap screws

Post by mcostello »

Can I have that #0000 in socket head set screw? What size Allen wrench is needed?
earlgo
Posts: 1794
Joined: Sat Jan 29, 2011 11:38 am
Location: NE Ohio

Re: Socket head cap screws

Post by earlgo »

My error. The #0000, #000, #00 screws are slotted fillister or flat head screws. The first SHCS McM-C lists is the #0 with a drive size at .050.
I've got a design going with the #12 screws, though. It is just a drill press stop spindle clamp, so no-one will know until the removal time comes. :lol:
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
earlgo
Posts: 1794
Joined: Sat Jan 29, 2011 11:38 am
Location: NE Ohio

Re: Socket head cap screws

Post by earlgo »

Cruising by the Tap display at the local ACE I was somewhat surprised to see a lone Irwin Hanson #14-20NS tap hanging there. The #14 screw is (14 x .013)+.060 inches in diameter or .242. So a #14-20 is approximately .008 less in diameter than a 1/4-20 UNC. Being curious, I checked the screw and bolt department and found no #14 screws. Quite a number of #12 Phillips head, though. If one searches on the internet the results generally come back as 1 4 - 20 and Amazon and others have 1/4-20 UNC fasteners, but no returns on the #14-20. Neither MSC or McM-C lists them.
Once again, why?
I'll keep my eyes open for a #16 tap.

It might be fun to make some kind of fixture kit with #14-20 tapped holes in it and supply the kit with 1/4-20 screws just to get a chuckle when assembly was attempted. :twisted:
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Socket head cap screws

Post by Harold_V »

It's been way too many years since I referred to the H28 Handbooks, but within them you are likely to discover why those odd threads used to be common, and why they are no longer readily available. Seems like the effort to standardize thread sizes came quite late in the scheme of things.

Another interesting thought. We often discuss imperial versus metric. The US has held steadfast with the Imperial system, but then, has it, really? The US gallon is not the same as the British gallon. Are they both considered Imperial?

Seems we have a blend of measuring systems.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Post Reply