Fastener and Thread Reference for Makers: Metric vs. Imperial, Tap and Drill Charts, and Torque Basics
Fastener sizing is one of those things every maker eventually has to look up, usually while standing at a hardware store aisle or halfway through a build with a stripped hole. Between 3D printing (heat-set inserts, M3/M4/M5 hardware everywhere), CNC and laser projects (T-nuts, machine screws, tap sizes for aluminum), and general shop work (wood screws, lag bolts, metric-to-imperial conversions on secondhand tools), the reference information is scattered and inconsistent across sources. This guide pulls the practical fastener and threading reference data into one place: metric vs. imperial systems, thread pitch basics, tap and clearance drill sizing, and torque guidance for the fastener sizes that actually show up in maker projects.
Metric vs. Imperial: Reading a Fastener Callout
Metric and imperial fasteners use different notation, and mixing them up is the single most common sizing mistake.
- Metric: written as Mdiameter x pitch, e.g. M5 x 0.8 means a 5mm nominal diameter thread with 0.8mm between thread crests. If pitch is omitted, it means "standard/coarse pitch for that diameter" — but always confirm, since fine-pitch metric fasteners (M5 x 0.5, for example) exist and are not interchangeable with coarse.
- Imperial (Unified): written as diameter-threads per inch, e.g. 1/4-20 means a 1/4" nominal diameter with 20 threads per inch. UNC (coarse) and UNF (fine) are the two common series — 1/4-20 is UNC, 1/4-28 is UNF.
- Small imperial sizes below 1/4" use a numbered system instead of a fraction — #4-40, #6-32, #8-32, #10-24 are the common maker-relevant sizes, and the number doesn't correspond to any obvious physical dimension, so it just has to be memorized or looked up.
Common Maker Fastener Sizes
SizeNominal DiameterWhere You'll See It M22.0mmSmall electronics enclosures, camera mounts M33.0mmMost common 3D printer/enclosure fastener; heat-set inserts, HAT standoffs M44.0mm3D printer frame hardware, mid-size enclosures M55.0mmCNC T-track hardware, gantry/frame assembly, Voron/CoreXY builds #4-40, #6-32~2.9mm, ~3.5mmUS electronics enclosures, rack hardware, older US-designed kits 1/4-206.35mmTripod mounts, T-track/jig hardware, US workshop fixturesTap and Clearance Drill Sizing
Two different drill sizes matter depending on what you're doing: a tap drill (slightly smaller than the fastener, so the tap can cut matching threads into the hole) and a clearance drill (slightly larger than the fastener, so the screw passes through freely and only threads into whatever's behind it).
ThreadTap Drill (mm)Clearance Drill (mm) M2 x 0.41.6mm2.4mm M3 x 0.52.5mm3.4mm M4 x 0.73.3mm4.5mm M5 x 0.84.2mm5.5mm M6 x 1.05.0mm6.6mm #6-322.85mm (#36 drill)3.9mm (#28 drill) 1/4-205.1mm (#7 drill)6.8mm (17/64")These figures target roughly 75% thread engagement, which is the generally accepted sweet spot — deeper engagement percentages barely add strength but make tapping dramatically harder and more likely to snap a small tap, especially in aluminum on a desktop CNC router where flute clearing is already marginal. For 3D-printed plastic, self-tapping directly into a printed hole (no separate tap) is common practice and the appropriate drill/hole size is usually closer to the screw's minor diameter rather than a metal tap-drill chart — consult your specific screw and printed material combination rather than using metal tapping figures.
Torque Guidance
Exact torque specs vary by fastener grade, material, and lubrication, so treat this table as a starting reference rather than an engineering spec — the fastener manufacturer's data sheet is authoritative when precision actually matters (structural builds, anything safety-critical).
FastenerTypical Torque (Steel into Steel/Aluminum, Class 8.8/Grade 5)Notes M31.0-1.3 N·mEasy to strip in aluminum or plastic — hand-tight plus a small turn is often enough M42.5-3.0 N·m M55-6 N·mCommon CNC gantry/frame bolt size M69-10 N·m 1/4-208-10 N·mFor anything going into 3D-printed plastic or a heat-set insert, torque specs from metal-to-metal charts don't apply at all — the practical limit is whatever the plastic or insert can withstand before stripping or pulling out, which is well below these figures and is more a matter of feel than a spec you can look up.
Thread Locking and Anti-Vibration
- Threadlocker (Loctite 243/blue, 271/red): use on fasteners subject to vibration — CNC gantry hardware, spindle mounts, anything on a machine that runs for hours. Blue (medium strength) is removable with hand tools; red (high strength) generally needs heat to break free and isn't appropriate for anything you'll need to service.
- Nylon-insert lock nuts: a mechanical alternative to threadlocker, good for fasteners you'll remove and reinstall repeatedly (workholding, adjustable jigs).
- Split lock washers: generally considered less effective than either of the above by modern fastener engineering consensus, though still common on older kits and hardware store assortments.
Metric-Imperial Conversion Quick Reference
MetricClosest Imperial M3Between #4 and #6 (not directly interchangeable) M4Close to #8, not a drop-in match M5Close to 3/16", not a drop-in match M6Close to 1/4", not a drop-in matchThe recurring theme in that table is "close, but not interchangeable" — metric and imperial threads are never truly compatible even when the diameters look similar, and forcing one into the other strips threads immediately. This matters most when working on secondhand tools or machines (an older CNC gantry, a vintage lathe) that may mix standards, or when a kit's hardware bag runs out and you're tempted to raid a mixed parts bin for a substitute.
None of this replaces checking the actual spec sheet for a critical fastener, but for the day-to-day question of "what drill bit do I need for this tap" or "is this a metric or imperial bolt," having the common maker sizes in one table saves a repeated trip to a search engine mid-build. Keep a printed or bookmarked copy of the tap-drill table taped inside a drawer near the drill press — it's the single most-referenced piece of shop reference material for most builders.