Thread - Pilot Drill Charts

[Jacques Reed]

Good Day All,

Just a slight diversion from topic but which many may find interesting.

After posting a picture of my numbered drill set I remembered that Ford carburetor jet sizes are given in number drill sizes. I know jet sizes have been covered before on MLU, but I thought I would see if any of my number drills matched an old Ford Holley carburetor jet I kept.
Many are missing from the set but #54 was there and a quick micrometer check confirmed it. The jet is numbered 054 which is the drill size.
I see on another MLU post the Ford CMP truck jet size was 050 except for the Workshop truck which was 053. Some American Flathead Ford sites specify 051 as standard, probably for cars. Quite a few sizes are available and it is a separate subject in its own right, but I thought others may find this interesting especially those new to the old Ford engines or just old engines in general.

So numbered drills are still being used in manufacturing, at least for replacement carby jets.

Cheers,

[Tony Smith]

Originally Posted by Jacques Reed

Good Day All,

Just a slight diversion from topic but which many may find interesting.

After posting a picture of my numbered drill set I remembered that Ford carburetor jet sizes are given in number drill sizes.

Cheers,

Not quite. The Holley Jet sizes closely correlate to thousandths of an inch; as the numbers go up, the Jets get bigger. Numbered drill sizes are related to wire gauges, as the numbers go up, the Drills get smaller. It was just a happy coincidence that your Number 54 drill fit a #54 Jet, as that is the point the two tables cross over.

BTW, never resize a jet with a drill bit. You will never get an accurate hole in the size you want. The WW2 Flathead Holley carburettors used jets and power valves that were standardised and are still used today in the latest Holley Quad Bore carbies. You can usually find a kit with a variety of different jet sizes to play with for a few dollars in most Auto Parts stores.

[Jacques Reed]

Tony,

Thanks for that information. Especially the availability of new Holley parts.
I stand corrected on the jet sizing misinformation. My bad.

Cheers,