Close, normal and free clearance-hole diameters for every metric screw size in the catalog, M1.6-0.35 to M24-3.0. Normal is the everyday choice; the last column gives it in inches too. Cutting threads instead? See the metric tap drill chart. Notes on each size follow the table.
Notes on these sizes
M1.6-0.35
M1.6 is instrument territory - camera internals, tiny hinges and connector hardware. At this scale a printed thread has nothing to grip, so the practical moves are drilling and tapping the printed part or gluing in a stud; most makers step up to M2 the moment the design allows.
M2-0.4
M2 turns up in drone frames, RC servos and small electronics sub-assemblies. Printed M2 holes close up fast - a printer that squeezes a tenth of a millimeter off a hole this small has taken more than four percent of it, which is why per-machine correction matters most at the bottom of the size range.
M2.5-0.45
M2.5 is the single-board-computer size - Raspberry Pi mounting holes are M2.5, and the cases, camera mounts and HAT standoffs around them inherit it, alongside PCB standoffs and micro servos. Self-tapping into a printed pilot works for light duty; a heat-set insert is the durable answer for anything you open twice.
M3-0.5
M3 is the default screw of the 3D-printing ecosystem - printer frames, extruder assemblies, electronics standoffs and most printed designs you download assume it. It is also the one size in the catalog with a second heat-set insert series to pick from, so a printed part with an insert usually beats a tapped plastic thread.
M3.5-0.6
M3.5 is the electrical-accessories size in much of the world - switch and socket plates thread onto M3.5 lugs, and small appliance covers use it too. Outside a wall box you rarely meet it, and that is the trap: eyeballed as M3 or M4, it jams or strips.
M4-0.7
M4 sits between electronics and structure - small brackets, cross-braces, printer bed hardware, RC chassis. It is big enough that a captured hex nut in a printed pocket carries real load, and small enough that the pocket still fits inside most walls.
M5-0.5
M5-0.5 fine shows up on optics, instruments and fine-adjust mechanisms where a full coarse pitch moves too far per turn, and in thin-wall tapping where a coarse thread would cut away too much material. Its tap drill is larger than coarse M5's - drill the coarse size for a fine tap and the tap binds.
M5-0.8
M5 is the aluminum-extrusion size - 2020 T-nuts on printer frames and CNC builds take M5, linear-rail hardware leans on it, and bike bottle-cage mounts are M5 as well. For frame-mounted printed accessories it is the size to design around.
M6-0.75
M6-0.75 fine is an adjustment-thread pitch - camera and optics mounts, measuring equipment, focus and leveling hardware. Fine pitches leave more core material, so the tap drill is larger than the coarse M6 number you probably have memorized.
M6-1.0
M6 is where fasteners start feeling structural - 3030 extrusion, machine guards, furniture fittings, load-bearing framing. A printed M6 joint rarely fails at the screw; it fails by pulling the head through the part, so pair the clearance hole with the head-pocket numbers below.
M8-1.0
M8-1.0 fine belongs to fine-pitch adjusters and thin-wall tapping - places where a coarse M8 thread would move too fast or bite too deep. Motorcycle and automotive hardware is where most people first meet it.
M8-1.25
M8 carries real load - caster stems, machine feet, furniture bolts, heavy frames. In printed parts M8 is usually a through-bolt with washers rather than a tapped thread: get the clearance right and let steel take the stress.
M10-1.0
M10-1.0 extra-fine is an instrument and optics pitch - fine adjusters and mounting bases. Three M10 pitches exist in the wild (1.0, 1.25 and 1.5) and they do not interchange - gauge the thread before you cut anything.
M10-1.25
M10-1.25 is the common automotive and motorcycle fine pitch - engine covers, brackets, frame hardware. Identify it carefully against its 1.0 and 1.5 siblings before tapping: the three look alike and fit nothing of each other's.
M10-1.5
M10 coarse is bracket-and-base territory - machine feet, heavy plates, structural anchors. Drilled steel takes the tap-drill number straight; a printed part this size is usually a jig, guide or template around steel hardware, riding on the clearance grades.
M12-1.25
M12-1.25 fine is an automotive pitch - many Japanese wheel studs and suspension bolts use it, along with spindle and axle hardware. Wheel hardware is safety-critical: match the existing pitch exactly, never re-tap to the pitch you happen to have.
M12-1.5
M12-1.5 fine is the other common automotive M12 - lug bolts and drain plugs on many European and Asian cars, plus hydraulic fittings. Its coarse sibling M12-1.75 is what the hardware store stocks; the two do not interchange.
M12-1.75
M12 coarse is the standard metric bolt of machine bases and structural brackets. At this size the clearance stack usually spans several parts - check the free grade before you commit a multi-hole bolt pattern to print.
M14-1.5
M14-1.5 fine is a lug-bolt and hydraulic-fitting pitch on many European cars, and an adjuster-nut thread in machine assembly. Fine M14 taps are not a hardware-store item - check tooling before you design around one.
M14-2.0
M14 coarse is uncommon outside machinery - heavy flanges, large brackets, structural bolting. Most home-machinist M14 work is repair, where the tap-drill number is the one that matters.
M16-1.5
M16-1.5 fine appears on machine spindles, bearing retainers and hydraulic adapters - threads that are assembled and adjusted rather than just clamped, where the finer pitch holds its setting.
M16-2.0
M16 is structural - steel connections, machine bases, lifting points. Nobody prints an M16 thread; the printed-part questions are clearance and head pocket, usually in a fixture that locates steel hardware.
M18-1.5
M18-1.5 is the automotive oxygen-sensor and drain-plug thread - if you are fixturing an O2 sensor bung or printing a sump-plug organizer, this is the page. Large fine-thread adjusters and machine spindles use it too.
M18-2.5
M18 coarse lives on large machinery mounts and heavy flange joints. Its fine-pitch sibling M18-1.5 is the automotive oxygen-sensor thread; this coarse version is the general-purpose one for taps and clearance work.
M20-1.5
M20-1.5 fine shows up on hydraulic ports, axle hardware and heavy fine-thread joints - machinery territory, where the finer pitch seals better and resists loosening.
M20-2.5
M20 is anchor-bolt and flange territory. If you are printing anything for M20 hardware it is a drill guide, a spacer or a protective cap - all clearance-fit problems, which is what the numbers below are for.
M22-2.5
M22 coarse is rare outside heavy structural bolting and rigging hardware. It earns its place in the catalog for the same reason the other odd sizes do: when you finally meet one, guessing the tap drill from memory is how taps break.
M24-2.0
M24-2.0 fine is machinery-only territory - spindle nuts, hydraulic adapters, large structural joints that need a fine thread. If a print is involved it is a fixture, and the clearance grades below are the working numbers.
M24-3.0
M24 is the largest size in the catalog - structural anchor bolts and heavy industrial framing. Printed parts meet it as sleeves, caps and alignment fixtures, all riding on the clearance numbers.
Metric and imperial clearances follow published mechanical-engineering references · heat-set pockets per CNC Kitchen · bearing housing seats follow published fit tables. Reference only - verify before you cut.