Holley Carburetor Jet Size Chart & Drill Size Guide
This guide provides a practical reference for Holley carburetor jet sizes and how they relate to common drill sizes used for cleaning, checking, and careful tuning work. Holley jet numbers are commonly used as fuel-flow references, so this guide should be used as a practical drill-size reference rather than a guaranteed manufacturer specification.
About Holley Carburetors
Holley carburetors are widely used in automotive, racing, hot rod, street performance, marine, and restoration applications. Many Holley carburetors use replaceable main jets identified by number, allowing tuners to make controlled fuel-metering changes by increasing or decreasing jet size.
Holley jet numbers are commonly discussed as if they correspond directly to drill sizes, but actual fuel flow can depend on more than hole diameter alone. Jet design, entry shape, exit shape, finish, and manufacturing differences can all affect flow. Always verify the specific jet and application before cleaning, checking, or modifying a carburetor jet.
Which Drill Set Is Right for Holley Jet Work?
For Holley carburetor jet checking, cleaning, and careful sizing work, choose a drill set based on the range of jet sizes you expect to work with.
Best Starting Point for Holley Jets: HS1 50 Pc Holley Carburetor Jet Drill Set
Covers a broad .040" through .125" range selected for many common Holley jet reference sizes. This is the best match for the Holley drill-size chart shown on this page.
Working on Smaller Carburetor Jets?
The 20 Pc Selected Sizes Carburetor Jet Drill Set covers selected sizes from .0135" through .071", useful for smaller carburetor jet work, small engines, motorcycles, scooters, and similar applications.
Need More Continuous Numbered-Drill Coverage?
The 25 Pc #75–#51 Carburetor Jet Drill Set gives a broader numbered-drill range for general carburetor jet checking, cleaning, and careful tuning.
Want Backup Drills in Each Size?
The D7 50-piece #80–#56 set includes 25 sizes with two drills per size, useful when working with small, brittle carbide drills and smaller jet ranges.
Not Sure Which Range You Need?
If you work on several carburetor brands, smaller jets, larger jets, Holley-style ranges, or Ford Model A Zenith carburetors, compare the full collection before ordering.
Important: carbide drills are brittle precision tools. Use light pressure, keep the drill straight, and avoid enlarging jets unintentionally during cleaning.
Holley Jet Size Chart & Drill Size Reference
Holley jets are identified by number, such as #60 or #70. These numbers are commonly used as practical jet-size references, but they should not be treated as exact drill-diameter specifications. Actual fuel flow can vary depending on jet design and condition.
| Jet Number | Approximate Size (Inches) |
|---|---|
| #40 | 0.040" |
| #50 | 0.049" |
| #55 | 0.052" |
| #60 | 0.057" |
| #65 | 0.063" |
| #70 | 0.070" |
| #75 | 0.076" |
| #80 | 0.093" |
| #85 | 0.096" |
| #90 | 0.101" |
| #95 | 0.104" |
| #100 | 0.128" |
Note: These values are approximate. Holley jet numbers are commonly associated with fuel-flow references, not guaranteed hole diameters.
Using Drill Sizes for Holley Carburetor Jet Work
Precision drill bits are commonly used in carburetor work for cleaning clogged jets, checking approximate jet size, comparing jet openings to known drill diameters, and carefully modifying jet orifices when tuning requires it.
Because drills come in fine size increments, they provide a practical way to work within carburetor jet size ranges. When modifying jets, make small changes and verify results carefully.
Practical Drill Size Range for Holley Jets
The chart below shows a practical drill size range covering many commonly used Holley jet references from 0.040" to 0.125".
Click the chart for a larger view.
This range covers many common Holley jet reference sizes, but always verify the actual drill diameter needed before modifying a jet. If you are unsure which set is best, compare the carburetor jet drill sets before ordering.
Choosing a Carburetor Jet Drill Set
Different carburetor jobs may require different drill ranges. A larger set gives you more coverage, while a smaller selected-size set may be enough for common cleaning, checking, or tuning work.
- HS1 50-piece Holley-focused set: covers the .040"–.125" range shown in this guide for broader Holley jet reference coverage. View HS1 set →
- 20-piece selected-size carburetor set: useful for smaller common carburetor jet work where you only need selected sizes. View 20-piece set →
- 25-piece carburetor set: covers a broader numbered-drill range for general carburetor jet checking, cleaning, and careful tuning. View 25-piece set →
- D7 50-piece #80–#56 set: includes 25 drill sizes with two drills per size, useful when you want backup drills in each size. View D7 set →
- Ford Model A Zenith set: selected for Ford Model A Zenith carburetor jet work. View Ford Model A Zenith set →
Compare Carburetor Jet Drill Sets
Tips for Jet Sizing and Modification
- Use light pressure when working with carbide drills
- Keep the drill straight to avoid making the jet opening oblong
- Always verify size before modifying a jet
- Make small, incremental changes when tuning
- Avoid enlarging jets unintentionally during cleaning
- When in doubt, replace the jet rather than over-drilling it
Conclusion
Understanding the relationship between Holley jet numbers and practical drill sizes can make carburetor cleaning, checking, and careful tuning more controlled. Use this chart as an approximate drill-size guide, verify the exact drill size before modifying any jet, and choose the drill set that best matches the range of sizes you need.