Close, normal and free clearance-hole diameters for every imperial screw size in the catalog, #0-80 to 5/8-11. Normal is the everyday choice; the last column gives it in mm too. Cutting threads instead? See the imperial tap drill chart. Notes on each size follow the table.
Notes on these sizes
#0-80
#0-80 is the smallest thread in the catalog - watch and instrument work, optics, the odd board-mount connector. Nothing about a printed #0 thread works; this page exists for drilling and tapping brass and aluminum at watchmaker scale.
#1-64
#1-64 is model-engineering and instrument scale. Taps this small break from side loads you cannot even feel - the right tap drill is the whole game, and it is smaller than the smallest bit in most drill indexes.
#1-72
#1-72 is the fine #1 - miniature instruments and model work where thread depth is scarce. It leaves more core material than 1-64, with the same fragile-tap warnings.
#2-56
#2-56 is the RC-linkage thread - clevises, pushrods and control horns standardized on it decades ago, and model kits still assume it. In printed parts it shows up in control surfaces and small brackets, where a clean clearance fit keeps a linkage slop-free.
#2-64
#2-64 fine is the quieter sibling of the RC-standard 2-56 - instrument work and precision brackets, mostly. Check which one you have before tapping; at this scale the pitch difference is invisible to the eye.
#3-48
#3-48 lives in model engineering, small covers and older instruments. The #3 size never won an ecosystem the way #2 (RC) and #4 (electronics) did, so you mostly meet it in legacy gear - exactly when a reference beats memory.
#3-56
#3-56 is the fine #3 - precision hardware and instrument covers, mostly in older equipment. If you are here you already know why; trust the numbers below over a worn chart taped to the drill press.
#4-40
#4-40 is the electronics thread - D-sub connector jackscrews, PCB standoffs, panel hardware and hobby servos all use it. It is the smallest size most makers tap regularly, and the one where a mis-sized pilot hole most often eats the tap.
#4-48
#4-48 fine appears in fine-thread panels, small enclosures and instrument hardware - places where 4-40 would be too coarse to hold its adjustment.
#5-40
#5-40 is the in-between size that never caught on - #4 and #6 took the ecosystems, so #5 survives in legacy equipment, light covers and the occasional captive screw. Identify it carefully: it measures between two sizes people actually stock.
#5-44
#5-44 fine is rarer still than 5-40 - instrument and legacy territory. The catalog carries it because misreading a #5 as a #4 or #6 is exactly how threads get stripped.
#6-32
#6-32 is the US electronics workhorse - PC cases and motherboard standoffs, wall plates and switch screws, speaker terminals. It is coarse for its diameter, which makes it easy to tap and easy to strip - in a printed part, give it a heat-set insert.
#6-40
#6-40 is the fine #6 - optical and camera mounts, fine-thread brackets, adjustment screws. Shallower flanks and more core material than 6-32, so its tap drill runs larger.
#8-32
#8-32 is the general-purpose US machine screw - enclosures, brackets, jigs and knobs. It is the default medium screw of American hardware: a step up from electronics sizes, a step below anything structural.
#8-36
#8-36 fine leans instrument and optical - mounts and fixtures where a #8 needs to hold a setting rather than just clamp. Most #8 hardware in the wild is 8-32; verify before you tap.
#10-24
#10-24 is builder-grade coarse - sheet-metal fastening, electrical gear, shelf standards, light framing. It taps easily in everything from pine to aluminum, which is why so many jigs and fixtures end up tapped #10-24.
#10-32
#10-32 is the fine #10 - avionics and camera hardware use it, and many equipment-rack rails are tapped 10-32. Rack work is the classic reason to keep its clearance number within reach.
#12-24
#12-24 is a rack-rail thread: where a US equipment rack is tapped rather than square-hole, 12-24 and 10-32 are the two you meet, and light machinery and appliance frames use it too. #12 is one of two sizes the ASME clearance tables skip, so the grades here come from Machinery's Handbook - a provenance note most charts leave out.
#12-28
#12-28 fine is genuinely rare - fine-thread appliance and machine hardware, mostly legacy. Like its coarse sibling 12-24 it falls outside the ASME clearance tables, so the grades here carry Machinery's Handbook values.
1/4-20
1/4-20 is the most recognizable thread in the US - the tripod socket on most cameras, T-slot fixture tables, hardware-store bolt bins. For printed camera and jig accessories, the clearance grades below decide whether the part slides over the stud or has to be forced.
1/4-28
1/4-28 fine is automotive and aircraft territory - grease-fitting (zerk) threads are 1/4-28, and AN hardware uses it throughout. It will start in a 1/4-20 hole and then bind - check the pitch before forcing anything.
5/16-18
5/16-18 is US general-purpose bolting one step up from 1/4-20 - machine bases, woodworking T-nuts, equipment guards. In printed fixtures it is a through-bolt size: clearance and head pocket, with steel doing the holding.
5/16-24
5/16-24 fine leans machine assembly and tooling, with a strong automotive presence in AN-style hardware. Fine threads at this size hold adjustment and resist vibration better than the coarse 18-pitch.
3/8-16
3/8-16 is the big-tripod and workholding thread - tripod heads, clamping kits and equipment mounts live on it. A printed adapter between 1/4-20 and 3/8-16 camera gear is a classic first print, and it lives or dies on these clearance numbers.
3/8-24
3/8-24 fine is automotive - brake and fuel fittings, AN hardware, spindle threads. Much of it lives in safety-critical systems: match the existing thread, never adapt it to what you stock.
7/16-14
7/16-14 is an equipment-and-structure size - machine assembly, trailer hardware, implement bolts. Less common than its 3/8 and 1/2 neighbors, which is exactly why the numbers are worth looking up rather than guessing.
7/16-20
7/16-20 fine is machine-assembly and automotive territory - wheel studs on many older US cars, hydraulic adapters, tooling. Meet it mostly in repair work, where identifying it correctly is half the job.
1/2-13
1/2-13 is serious-bolt territory - heavy vises, machine foundations, structural anchors. Printed parts at this size are jigs, caps and spacers around steel hardware; the clearance grades are the working numbers.
1/2-20
1/2-20 fine is automotive and tooling grade - spindles, wheel studs on older vehicles, fine-thread structural joints. The hardware store stocks its coarse sibling 1/2-13; this one you order.
9/16-12
9/16-12 is the odd one out - big enough for machine bases and equipment frames, rare enough that the ASME clearance tables skip it. The grades here carry Machinery's Handbook values instead, one of two sizes in the catalog where that provenance applies.
5/8-11
5/8-11 is workholding scale - T-slot clamping studs, machine anchors, rigging hardware. If you are printing for it, it is a drill guide or a protective cap, and the free grade is usually the right clearance call.
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.