The Stovebolt Site Forums The Shop Area Engine Shop Carburetor screw size??

So I picked up a couple of Rochester B’s at the Pete swap meet at Texas motor Speedway this past weekend. Both are complete, and appeared to be in pretty good shape except that on one of them the 4 screws that hold the airhorn to the fuel bowl are buggered up and I’d like to replace them at the same time I rebuild the carb. I’ve been told they are “Fillister” screws, but I don’t know any more than that. Can someone please tell me the size and thread count? I can figure out the length.

Thanks!

Fillister is the head style. (like pan head, flat head, button head) Contact Mikes Carburetors for screws for B1. Don't take this the wrong way but since you have at least 4 classics, you need a tap and die set which will have a thread gauge in it. That tells you the threads per inch. You need calipers which tells you the size and, like you said, the length is easy. That's how it's done. Then you search fastener websites and order or go to the hardware store. We all have lots of times we need to know screw or bolt sizes and threaded hole sizes to either buy hardware or chase threads. (with the tap and die set). The calipers and tap and dies have many other uses also. No need for special gauges.

Original carburetor screws are, in fact, sometimes hard to find. Mike will have them. He has excellent videos online on B1 rebuilding and has the rebuild kits.

No. 4 is .112 diameter
6 is .138
8 is .164
10 is .190 and so on into the fractions

http://www.carburetor-parts.com/Screws_c_951.html

To whom it may concern:
There are many tap and die sets. Most of them have round dies. If you are only going to buy one in your life, buy a set with hex shaped dies. They are more positive drive and can be used with a ratchet wrench and socket.
https://www.amazon.com/ABN-Titanium...p;sr=8-69&keywords=taps+and+dies+set

I’m assuming you are familiar with these carbs, but if not, address any warpage while you have them apart. The rest should be straight forward.

No. 12 - 28 x length.

I buy them at my local hardware store.

Depends entirely on WHICH Rochester B. As Tom (above) mentioned, some used 12x28. Others used 10x32. To know for certain, either measure with micrometer, or look up bill-of-materials based on tag number.

The fillister head is the thicker head (withstands more torque).

Finish on 1950~1955 was yellow zinc. Finish after 1955 was black oxide.

We quit selling the screws as we no longer can purchase "made in USA"; and the off-shore versions seem to be inferior quality.

One of the other issues with the Rochester B's is the zinc alloy was softer than that in other makes of carburetor. Have seen lots of B's that required either drilling and retapping to the next larger size, or installation of heli-coils.

As Bart suggested, a thread pitch gauge is a useful tool; and if you have to have off-shore, the off-shore dial calipers are quite inexpensive. Personally, I prefer Starrett.

Enjoy.

Jon.

You can also do it the old fashioned way. Take the carb to the hardware store and find a screw that fits and looks right.

Thanks Jon, Bartamos and Tom for the nice information and links. Since I don’t have a dial caliper or a screw thread gauge the best thing for me to do is to take my Fillister head screws to a local fastener company and ask them to measure them and match them up with new ones. I would never have guessed Rochester would have used different size screws!

And thanks Lindsey for reminding me to check for warpage.

They made a design change in 1952 to larger screws, bigger bosses and thicker flange because of "warpage" which was really deflection/bending of screw bosses. Seems like that would be the No. 12-28 screws Jon mentioned. Probably a good way to see if you have a "stronger" redesigned B1. Measure a screw.

Didn’t know about the 1952 design change. Thanks for the comments.

The No. 10 - 32 that Jon mentioned for the air horn
is also the same screw used to attach the main well support.

Therefore, the main well support screw will attach your air horn
if you have No. 10 - 32 air horn screws.

Chevrolet lists the;
No. 10 - 32 length at 9/16.
No. 12 - 28 length at 15/16.

Both screws should have a washer.

Thanks Tom. This morning I stopped by Ace Bolt & Screw here in San Antonio to see if they had some. Closest they had was the correct thread count & length, but the top is round and has a socket for an Allen wrench. It’s black anodized. It will work just fine but won’t look original. I’ll keep looking locally until I’m forced to order from an online vendor.

Try

McMaster carr

...click...

There are some correct-appearing fillister head screws on Ebay with the right thread- - - - -saw them yesterday.
Jerry

Thanks for the link Dads50. Excellent website!!

Jerry....I’m going on EBay right now. Thanks!

Still there- - - - -a pack of 10, I believe, for about 9 bucks! 12-28 X 1" Fillister head screws.
Jerry

Looks like the 12-28x1 fillister is common in the firearms industry.
Brownells Firearms

Maybe your local gun shop has them.