Okay, let's talk brass tacks. That 6-32 screw you're trying to tap threads for? Mess up the pilot hole and you'll either snap your tap or end up with threads weaker than cheap coffee. Been there, done that, broke three taps before I figured this out. The drill bit size for 6-32 tap jobs isn't some mystery, but get it wrong and you'll regret it big time.
Look, I remember trying to assemble a camera rig years back. Needed twelve perfect 6-32 threaded holes in aluminum. Grabbed what I thought was close enough from my drill index. Five holes in, *snap* - there went my first tap. After some colorful language and a trip to the hardware store, I learned the hard way that "close enough" ruins your workpiece and wastes money.
What Does "6-32" Actually Mean?
Before we dive into drill bit sizes, let's clear up what those numbers mean. The "6" is the screw diameter size (about 0.138 inches if you're curious), and "32" means 32 threads per inch. These guys are everywhere - electronics enclosures, 3D printer parts, guitar tuners, you name it. They're the workhorse of small assemblies.
Materials Change Everything
What you're drilling into matters way more than most guides tell you. Drill the same size hole in stainless steel as you would in pine wood? Prepare for disaster. Harder materials need slightly larger holes because the tap can't displace as much material without breaking. Softer stuff needs tighter holes or your threads won't grip.
Pro Tip: Always drill a test hole in scrap material identical to your workpiece. Saves headaches and broken tools.
The Exact Drill Bit Size for 6-32 Tap
Alright, here's what you actually came for. After snapping more taps than I care to admit, here's the definitive answer:
| Measurement System | Exact Size | Practical Equivalent | Notes |
|---|---|---|---|
| U.S. Fractional | - | 7/64" (closest common) | Actually 0.0035" oversized |
| U.S. Numbered | #36 | - | Perfect match at 0.1065" |
| Metric | 2.70mm | 2.7mm (common) | 2.75mm acceptable in soft materials |
| Decimal Inch | 0.1065" | 0.107" | Marginally oversized |
Here's the kicker: If you only remember one thing, make it #36 drill bit for 6-32 tap applications. Why? Because it's dead on 0.1065 inches - the exact size needed for perfect 75% thread engagement. Perfect balance between strength and avoid breaking taps.
When You Absolutely Need Perfect Threads
For critical applications (think aircraft parts or medical devices), engineers calculate drill sizes using this formula:
Drill Size = Major Diameter - (0.6495 × Pitch)
Plugging in for 6-32:
- Major Diameter = 0.1380"
- Pitch = 1/32 = 0.03125"
- Drill Size = 0.1380 - (0.6495 × 0.03125) = 0.1380 - 0.0203 = 0.1177"? Wait no...
Hold up - something's off here. I used this formula once and ended up with a hole way too big. Turns out I confused minor diameter with major. Let me correct that:
Actual formula: Drill Size = Major Diameter - (1.0829 × Pitch)
For 6-32:
- 0.1380 - (1.0829 × 0.03125) = 0.1380 - 0.03384 = 0.10416"
But #36 is 0.1065"? Close but not exact. Truth is, industry uses standardized drill sizes rather than theoretical calculations. The #36 accounts for real-world tapping dynamics better than pure math.
Drill Bit Size for 6-32 Tap Based on Material
This is where most tutorials drop the ball. Same hole size for plastic and stainless steel? Terrible idea. Through painful experience, here's what actually works:
| Material Type | Recommended Size | Adjustment | Why It Matters |
|---|---|---|---|
| Aluminum/Soft Metals | #36 (0.1065") | None needed | Prevents loose threads |
| Mild Steel | #36 (0.1065") | None | Balance of strength & ease |
| Stainless Steel/Titanium | #37 (0.1040") | -0.0025" | Reduces tap breakage |
| Plastics/Acrylic | #35 (0.1100") | +0.0035" | Prevents material cracking |
| Hardwoods | #36 (0.1065") | None | Optimal grip |
| Cast Iron | #36 (0.1065") | None | Standard works well |
I learned the stainless steel lesson the hard way. Was building a custom motorcycle bracket from 304 stainless. Used standard #36 drill bit for 6-32 tap. Third hole in, *ping* - $12 tap gone. Switched to #37 and finished the job without casualties.
Step-by-Step: Drilling Perfect Holes for 6-32 Tapping
Tools aren't magic wands. Here's how to actually do it right:
Essential Tools
- Drill press (hand drill works but precision suffers)
- #36 HSS drill bit (carbide for hard materials)
- Center punch
- Cutting fluid (WD-40 for aluminum, Tap Magic for steel)
- Solid workpiece clamping
- 6-32 taper tap (starter) and plug tap (finisher)
Drilling Process
- Mark your spot - Center punch with authority. Skimp here and your drill wanders.
- Clamp like it owes you money - No exceptions. Workpiece movement ruins holes.
- Lubricate before drilling - Even for wood. Reduces heat and splintering.
- Drill speed matters:
- Aluminum: 3,000 RPM
- Steel: 1,500 RPM
- Stainless: 800 RPM
- Peck drill technique - Drill 2x diameter depth, back out to clear chips. Repeat.
- Debur holes immediately
Warning: That drill bit for 6-32 tap work must be sharp. Dull bits make oversized holes. Check yours under magnification - if the edges look rounded, replace it. I keep dedicated #36 bits just for tapping.
Why Your Tap Keeps Breaking (And How to Stop It)
Snapped taps make me furious. Here's why it happens with 6-32 specifically:
- Chip buildup - Tiny flutes clog instantly. Solution: Back out every 1/2 turn to break chips.
- Misalignment - Even 2° off and stress skyrockets. Use a tapping guide.
- Poor lubrication - Dry tapping is tool murder. Different fluids for different materials:
| Material | Best Lubricant | Cheap Alternative |
|---|---|---|
| Aluminum | WD-40 | Kerosene |
| Steel | Tap Magic | Motor oil |
| Stainless | Moly-Dee | Crisco (seriously) |
| Plastic | Water | Spit (no joke) |
6-32 Tap Drill Size FAQ (Real Questions from My Workshop)
These come up constantly in forums and my shop:
Question: Can I use 7/64" instead of #36?
Technically? Yes. 7/64" is 0.1094" vs #36's 0.1065". But that 0.0029" difference creates significantly weaker threads - about 15-20% less holding power. Only acceptable in non-critical soft materials. I'll occasionally do this in pine for jigs, never in metal.
Question: What if I don't have a #36 drill bit?
Options in order of preference:
- 2.7mm metric bit (0.1063" - near perfect)
- 2.75mm metric bit (0.1083" - slightly loose)
- #37 (0.1040") + careful hand reaming
- 7/64" (0.1094") + thread locker compound
Question: Why does my 6-32 screw feel loose?
Three likely culprits:
- Drill bit for 6-32 tap was too large (measure it!)
- Tapping wasn't perpendicular (threads stripped)
- Material compression (common in plastics/soft woods)
Question: Can I tap without a drill press?
Yes, but brace yourself. Hand drill tapping 6-32 threads requires:
- Center punch DEEP
- Drill guide attachment
- 90° angle indicator
- Patience of a saint
Even then, expect 20% failure rate in hard materials. My first year apprentice work had more crooked holes than a politician.
Advanced Techniques for Perfect Threads
Once you've mastered basic drill bit size for 6-32 tap work, level up:
Thread Depth Ratios
How deep should threads go? Rule of thumb:
- Steel: 1.5x bolt diameter deep = 0.207"
- Aluminum: 2x diameter = 0.276"
- Plastic: 3x diameter = 0.414"
But for 6-32 specifically, minimum engagement is 0.125" for structural connections. I mark my taps with tape at these depths.
Through Holes vs Blind Holes
Blind holes (non-through) need special care:
- Drill 1.5x deeper than needed threads
- Use spiral point taps (gun taps)
- Compressed air chip clearing after every 2 turns
My worst tap breakage happened in a blind hole in 4140 steel. Took an EDM machine to remove it - $200 lesson.
When to Use Thread Inserts
Sometimes tapping directly is dumb:
- Soft materials (balsa, PVC)
- Frequent disassembly points
- Overloaded threads
For 6-32 size, Keenserts are my go-to. Drill with #22 bit (0.157"), tap 1/4-28, insert steel insert. Bulletproof.
Drill Bit Types Compared for 6-32 Work
Not all bits are equal for tap drilling:
| Bit Type | Best For | Worst For | Cost | My Rating |
|---|---|---|---|---|
| HSS Twist Drill | General use | Hardened steel | $ | ★★★☆ |
| Cobalt | Stainless/tough alloys | Wood/plastics | $$ | ★★★★ |
| Carbide | Production work | Hand drilling | $$$$ | ★★★☆ |
| Brad Point | Wood/acrylic | Any metal | $$ | ★★☆☆ |
| Jobber Length | Deep holes | Precision work | $$ | ★★★☆ |
Truth time: I mostly use cheap HSS bits but replace them twice as often. Carbide snaps too easily in small sizes. Once snapped a $35 carbide #36 bit in 6061 aluminum because my drill chuck had runout. Still makes me wince.
My Workshop Wisdom: Lessons from Broken Taps
After twenty years of threading holes:
- Buy quality taps - Irwin or Greenfield. Cheap taps are false economy.
- Keep bits organized - Dedicate a drill index section to tap sizes.
- Mark depth clearly - Paint marker on drill bit saves miscues.
- Wear eye protection ALWAYS - Broken taps become shrapnel.
- Walk away when frustrated - Force leads to broken tools.
Finding the right drill bit size for 6-32 tap work transformed my metal projects from frustrating to flawless. When that screw threads in smooth with solid resistance? Pure satisfaction. With these guidelines, you'll achieve that consistency.