Name of this type of screw.

I'm rebuilding a Holley 4160 carb. Made in 1976. And the secondary metering plate is held on with weird looking screws:



What is the name of this type of screw?

I've heard them called "clutch-head" screws but noone around here (Vancouver Canada) seems to have heard of them before.

 

clutch

 

http://www.google.com/search?q=clut...SYD67XiAKszLmqDQ&ved=0CF4QsAQ&biw=892&bih=425
lots of stuff here.
They sure look like clutch heads to me.

 

Clutch head. Chevy was big on them in the 30's-40's. I guess they were also used in the RV industry. Do a search there should be plenty of info. Yes drive bits are available.

 

Those are the ones that will accept a sharp drill bit in my shop!!!

 

Yep, clutch head. My 50 chevy is loaded with them. Go to Harbor Freight, pick up their bit set. It is like 10 bucks for 100+ pieces. It has all of the clutch sizes in it.

 

Does that mean you'd drill them out and replace them with something else?

 

a small screwdriver will work if it fits tight.

 

Since it's on a carb, I'd reuse them if you have the right bit, otherwise those get drilled out at my place!!

 

my '60 elco still has some in there too.

 

Brilliant design in my opinion. Almost never strip, and keep tool centered on head. Can't say that for Slot (tool slip), Allen (circular design strips easy), or Phillips (low contact profile strip prone). Robertson (square), is my second favorite. Capitalism at its finest.

 

Square is Robertson isn't it?

 

robertson is what we always called them square headed screws.phillips can be a pain when they strip,like robertsons,clutch head hold very well.i have a set of those bits in my set,never used them,probably never will

 

Yes, and they are found on Model A Fords built in Canada. The design is very popular now with deck screws.http://en.wikipedia.org/wiki/List_of_screw_drives

 

Yup "Clutch Head"


I found this to be true also
and some of the square bits fit some of them, well if you force them just a bit, ability to get them to back out is dependent upon if its rusted in place or in some cases dis-simular metal corrosion can sometimes get a good hold on them

 

I've seen clutch head screwdrivers at my local ACE hardware. they are not too common, other than those multi bit sets you see around.

 

neat history of clutch head screws in GM vehicles vs. phillips screws, it involved lawsuits and patents, good info to google.

 

late 30' -? GMC trucks used phillips screws, chevy trucks used clutch head [one way of telling them apart ]. i bought a set of clutch head screwdrivers but they were shaped more like a bow tie [round center] they would not fit the early screws so look for this when buying them.

 

My 46 chevy is full of these. They are clutch heads and someone sold them to GM before the war. Would have been a ome run except the Phillips screw, screwed them. GM used up their stock by 1950. Snap on Harbor Freight or Jim Carpenter have them. They are a pain! And there is at least 3 sizes maybe 4!

 

I believe Sears still sells clutch head screw drivers. I have three different sizes that I got from them.

 

Here's a chart for future reference ! www.zoice.com/2009/01/04/screw-head-classifications/

 

Thanks!

 

I was told GMC's had lock washers, Chevies don't, another was to tell them apart, if all evidence has rusted away.

 

In the past they were also called "figure 8" screws and some tool manufacurers even called them "Chevrolet screws".

 

Butterfly Clutch (type G) is what you are looking for. Holley is a #6 (5/32)
The pic above has GM style and not what you have. Have done 3 of those carbs in last week or so.

Even the Ford/Holley carbs thru 1986 used that style screw on transfer plate.
First used in 1959 (Edsel Carb) probably still used in some Holley's today.

Edit: just found this--- http://www.jalopyjournal.com/forum/showthread.php?t=135697

http://www.jalopyjournal.com/forum/showthread.php?t=602373

 

If you're looking for a tool to remove/re-install those, take an old worn out screw driver and grind it to fit those clutch heads. Easy.

 

Clutch head screwdrivers and bits are always on eBay. Thats where I got mine.