Metric Thread Pitch Chart — Coarse and Fine Pitch for Every Size, With the Inch UNC / UNF / UNEF Series

Metric Thread Pitch Chart — Coarse and Fine Pitch, M1 to M64

Every metric size has one coarse pitch (ISO 261) and one or two fine pitches that bolts and nuts are made in (the ISO 262 selection); M10, for example, is 1.5 mm coarse and 1.25 mm or 1 mm fine. M7 has a standard thread but no standard hex bolt; bolts in M7, M9 and M11 are made to order (see odd metric bolt sizes). EKINSUN LTD is a custom parts manufacturer that cuts coarse, fine and inch threads to order and makes coarse-to-fine adapters, studs and nuts from 1 piece.

Coarse pitch per ISO 261; fine pitches per the ISO 262 selection. ISO 261 defines more fine pitches than the ones listed, for example M10 × 0.75, M12 × 1 and M16 × 1; we cut those as well. A size written without a pitch, such as M12 × 40, is coarse. Tap drill sizes for coarse and fine threads are on the clearance hole and tap drill chart; pitches above M64 on fine pitch above M64; standard bolt lengths for each size on the bolt length chart.

Inch Thread Pitch Chart — UNC, UNF and UNEF

Inch threads are counted in threads per inch (TPI): UNC is the coarse series, UNF the fine and UNEF the extra-fine, and the pitch in millimetres is 25.4 divided by the TPI. A 1/4 in bolt is 1/4-20 UNC or 1/4-28 UNF; sizes below 1/4 in are numbered from #0 to #12.

Threads per inch per ASME B1.1. #0 exists only as #0-80 UNF. Metric and inch threads that look alike (M6 and 1/4-20, M12 × 1.75 and 1/2-13) are compared on the metric vs imperial thread chart; British threads on the Whitworth thread chart. Hydraulic JIC, AN and ORB fittings use UNF and UN threads by dash size (-6 is 9/16-18, -8 is 3/4-16): see the JIC and ORB fitting size chart.

How to Measure Thread Pitch — Ten Threads Over a Rule

A caliper and a steel rule are enough to tell coarse from fine and metric from inch. Measure the outside diameter of the bolt with the caliper, then lay the rule along the thread and read the length of ten threads from crest to crest; ten threads divided by ten is the pitch. A diameter that is not a round number of millimetres points to an inch thread; for inch threads 254 divided by the ten-thread length gives the threads per inch. A thread gauge confirms the reading: the right leaf sits in the thread with no light between the teeth. Check the direction too: a left-hand thread rises to the left when the bolt is held upright.

Coarse vs Fine Thread — Strength, Travel per Turn and Where Each Is Used

A fine thread of the same diameter has a larger tensile stress area, so in the same property class it carries more tensile load: M10 × 1 has 64.5 mm² against 58.0 mm² for M10 × 1.5. The stress area is calculated from the pitch and minor diameters as ISO 898-1 defines it; the values below reproduce the ones printed in the standard.

Coarse-to-Fine Thread Adapters — Same Diameter, Different Pitch

A coarse-to-fine thread adapter joins two threads of the same diameter and different pitch, such as M10 × 1.5 to M10 × 1.25 or 1/2-13 UNC to 1/2-20 UNF. It is used where a part with a fine thread has to take a standard coarse bolt or fitting, or the other way round, and neither part can be re-threaded. We make it as a male-female adapter, a female-female coupling or a male-male stud, with a hex or flats for a spanner, from 1 piece.

Materials: 304 (1.4301) or 316L (1.4404) stainless, brass CW614N, 42CrMo4 alloy steel for load-bearing studs, and 6061 aluminium for light-duty adapters such as instrument mounts. Adapters between two different diameters are on custom metric thread adapters and thread adapters; couplings with a different thread at each end on double-ended studs.

For a pitch the chart does not list, the basic-profile values are worked out from the same constants: the M27×1.75 thread dimensions page gives pitch diameter, minor diameters, tap drill and wire size for that special pitch.

On the Shelf or Made to Order

Standard coarse and fine bolts and nuts are shelf parts and cost less than any machined part. We supply standard sizes too, and for one piece needed today a local store is quicker. We make the threads and pairs the shelf does not carry, from 1 piece.

Thread Pitch by Size — Quick Answers

What is the thread pitch of M3?

M3 has a coarse pitch of 0.5 mm, so ten threads measure 5 mm; its fine pitch is 0.35 mm (ten threads = 3.5 mm).

What is the thread pitch of M4?

M4 has a coarse pitch of 0.7 mm, so ten threads measure 7 mm; its fine pitch is 0.5 mm (ten threads = 5 mm).

What is the thread pitch of M5?

M5 has a coarse pitch of 0.8 mm, so ten threads measure 8 mm; its fine pitch is 0.5 mm (ten threads = 5 mm).

What is the thread pitch of M6?

M6 has a coarse pitch of 1 mm, so ten threads measure 10 mm; its fine pitch is 0.75 mm (ten threads = 7.5 mm).

What is the thread pitch of M8?

M8 has a coarse pitch of 1.25 mm, so ten threads measure 12.5 mm; its fine pitches are 1 mm (ten threads = 10 mm) and 0.75 mm (ten threads = 7.5 mm).

What is the thread pitch of M10?

M10 has a coarse pitch of 1.5 mm, so ten threads measure 15 mm; its fine pitches are 1.25 mm (ten threads = 12.5 mm) and 1 mm (ten threads = 10 mm).

What is the thread pitch of M12?

M12 has a coarse pitch of 1.75 mm, so ten threads measure 17.5 mm; its fine pitches are 1.5 mm (ten threads = 15 mm) and 1.25 mm (ten threads = 12.5 mm).

What is the thread pitch of M14?

M14 has a coarse pitch of 2 mm, so ten threads measure 20 mm; its fine pitch is 1.5 mm (ten threads = 15 mm).

What is the thread pitch of M16?

M16 has a coarse pitch of 2 mm, so ten threads measure 20 mm; its fine pitch is 1.5 mm (ten threads = 15 mm).

What is the thread pitch of M20?

M20 has a coarse pitch of 2.5 mm, so ten threads measure 25 mm; its fine pitches are 2 mm (ten threads = 20 mm) and 1.5 mm (ten threads = 15 mm).

What is the thread pitch of M24?

M24 has a coarse pitch of 3 mm, so ten threads measure 30 mm; its fine pitch is 2 mm (ten threads = 20 mm).

What is the thread pitch of M30?

M30 has a coarse pitch of 3.5 mm, so ten threads measure 35 mm; its fine pitch is 2 mm (ten threads = 20 mm).

What is the thread pitch of a 1/4 in bolt?

A 1/4 in bolt is 1/4-20 UNC coarse, a pitch of 1.270 mm (ten threads = 12.70 mm), or 1/4-28 UNF fine, 0.907 mm (ten threads = 9.07 mm), and the UNEF extra-fine thread is 1/4-32 (0.794 mm).

What is the thread pitch of a 3/8 in bolt?

A 3/8 in bolt is 3/8-16 UNC coarse, a pitch of 1.588 mm (ten threads = 15.88 mm), or 3/8-24 UNF fine, 1.058 mm (ten threads = 10.58 mm), and the UNEF extra-fine thread is 3/8-32 (0.794 mm).

What is the thread pitch of a 1/2 in bolt?

A 1/2 in bolt is 1/2-13 UNC coarse, a pitch of 1.954 mm (ten threads = 19.54 mm), or 1/2-20 UNF fine, 1.270 mm (ten threads = 12.70 mm), and the UNEF extra-fine thread is 1/2-28 (0.907 mm).

What to Send for a Quote

Both threads (size and pitch, or size and threads per inch), male or female on each end, the overall length and the length of each thread, the hex size if there is one, the material and the quantity. For a replacement, a photo of the part beside a rule and a ten-thread reading are enough. Made from 1 piece; quote in 12 hours.

How deep a thread has to go into an aluminium or a steel plate, 2 × d or 1 × d, is on plates with tapped holes.

Thread Pitch FAQ