English 
Views: 0 Author: Site Editor Publish Time: 2026-08-29 Origin: Site
Nut size | Thread diameter (d) | Wrench size / across-flats (W) | Nut height (m) |
|---|---|---|---|
M3 | 3 mm | 5.5 mm | 2.4 mm |
M4 | 4 mm | 7.0 mm | 3.2 mm |
M5 | 5 mm | 8.0 mm | 4.0 mm |
M6 | 6 mm | 10 mm | 5.0 mm |
M8 | 8 mm | 13 mm | 6.5 mm |
M10 | 10 mm | 16 mm | 8.0 mm |
M12 | 12 mm | 18 mm | 10.0 mm |
M16 | 16 mm | 24 mm | 13.0 mm |
M20 | 20 mm | 30 mm | 16.0 mm |
M24 | 24 mm | 36 mm | 19.0 mm |
Values per ISO 4032 (regular hex nut, style 1). The wrench size is always identical to the matching bolt's across-flats, so one wrench size fits both.
Jam nuts (thin hex nuts, ISO 4035) — about half the height of a regular nut (M8: 5.0 mm). Used as lock nuts or where space is tight.
Nylon insert lock nuts (DIN 985 / ISO 10511) — same across-flats and overall height as regular nuts; the nylon collar prevents loosening under vibration.
Flange nuts (DIN 6923) — wider across-flats than regular nuts (M8: 14 mm) with an integrated washer face.
Hex coupling nuts (DIN 6334) — elongated nuts used to join two threaded rods; same wrench size as the regular nut.
Wing nuts (DIN 315) — sized by thread only (M6, M8, M10); no wrench needed.
Match the thread — M8 nut goes on M8 bolt. Never force an M8 nut onto an M8 fine-pitch bolt (M8×1.0): the nut must match the pitch too, not just the diameter.
Check the height — standard nuts (ISO 4032) are fine for most joints. For high-vibration applications, use a lock nut or add a spring washer.
Strength class — nuts are marked with a number (e.g. 8, 10). An "8" nut pairs with grade 8.8 bolts; "10" with 10.9 bolts. Never pair a low-grade nut with a high-grade bolt — the nut becomes the weak link.
Choose the finish — zinc-plated for indoor, hot-dip galvanized or stainless 304/316 for outdoor and marine.
Mixing metric and inch — an M8 nut (13 mm wrench) is close to a 5/16" nut, but the threads are different. They will not fit properly and can cross-thread.
Ignoring pitch — M8 coarse (1.25) and M8 fine (1.0) nuts look identical; check the pitch before installing.
Reusing nylon lock nuts — the nylon collar only locks once; replace after removal.
Pairing by wrench size instead of thread — a 13 mm wrench fits M8 nuts, but 13 mm is also used by some inch sizes; always confirm the thread, not the wrench.
Q1: What size wrench fits an M8 nut? 13 mm — the same across-flats as an M8 bolt.
Q2: How do I read a nut size like "M10"? M10 = 10 mm thread diameter. It fits an M10 bolt and takes a 16 mm wrench.
Q3: What's the difference between a regular nut and a jam nut? A jam nut is roughly half the height, used to lock another nut or for limited space.
Q4: Which nut grade matches an 8.8 bolt? A nut marked "8" (property class 8, per ISO 898-2).
Q5: Can I use an M8 nut on an M8 fine thread bolt? Only if the pitch matches — M8 coarse (1.25) and fine (1.0) nuts are different parts.
Q6: What's the strongest common nut type? For high-vibration joints, a nylon insert or flange lock nut retains clamping force better than a plain hex nut.
Ningbo Weifeng Fastener Co., Ltd. manufactures hex nuts (ISO 4032, DIN 934, GB/T 6170), jam nuts, nylon insert lock nuts, flange nuts and coupling nuts in sizes M3–M64, grades 4–12, zinc plated, hot-dip galvanized or stainless steel (304/316) — browse our hex nut range or send us your size and quantity for a quote.
Sources: ISO 4032/4035 (hex nuts), ISO 898-2 (nut property classes), DIN 934, DIN 985, GB/T 6170/6175, ANSI/ASME B18.2.2 (inch nuts).
