JIS hardware for classic Japanese cars
Japanese cars have been built with JIS hardware since the 1960s, and many still are. The threads are metric, but the head sizes, strength marks and finishes follow the Japanese standard rather than the ISO sizes on hardware-store bolts. Boltright supplies it bagged and labelled, by car or by thread size.
That covers JIS bolts, JIS nuts, JIS screws and the washers that go with them: hex bolts, flange bolts, SEMS screws with captive washers, Phillips screws, nyloc and flange nuts, spring washers and flat washers. If you are hunting for Japanese bolts for a JDM restoration that a hardware store cannot match, this is what you are looking for.
JIS head sizes
These are the usual hex head sizes on JIS bolts, next to the size you would find on a modern metric bolt.
| Thread | JIS head | Common ISO head |
|---|---|---|
| M3 | 5.5 mm | 5.5 mm |
| M4 | 7 mm | 7 mm |
| M5 | 8 mm | 8 mm |
| M6 | 10 mm | 10 mm |
| M8 | 12 mm | 13 mm |
| M10 | 14 mm | 16 or 17 mm |
| M12 | 17 mm | 18 or 19 mm |
Kits by car
| Car | Kit |
|---|---|
| Datsun 240Z, 260Z, 280Z (S30) | S30 Big Bolt Kit and Small Bolt Kits, available now |
| Any classic Japanese car | M6 Resto Kits, available now. M8 coming soon |
| Datsun 280ZX (S130) | Being considered |
| Toyota Celica TA22 | Coming soon |
| Subaru Impreza GC8 | Coming soon |
Kits by thread size
The M6 Resto Kits are not tied to one car: they hold the M6 JIS hardware any classic Japanese restoration goes through, in yellow or blue zinc, M8 Resto Kits with 12 mm JIS heads are coming soon, along with M10, M5, M4 and smaller, and a self-tapping screw kit.
Strength marks and finishes
Some JIS bolts carry a 4 or a 7 on the head to show strength. Factory finishes were mostly zinc with a yellow, blue or clear chromate, with black on some parts. Matching both keeps the car correct and stops rust coming back. More detail in JIS vs metric bolts.
Questions
What is JIS hardware?
Fasteners made to the Japanese Industrial Standards, used on Japanese cars from the classics through to many current models. The threads are metric, but bolt heads are often a size smaller than ISO metric bolts.
What spanner fits a JIS M8 bolt?
12 mm. A modern ISO M8 bolt usually has a 13 mm head.
Can I use normal metric bolts instead?
The thread will fit, but the head size, strength and finish often will not match, and a larger head may not clear nearby parts.
What do the 4 and 7 marks mean?
They are strength marks stamped on the bolt head. A 7 mark bolt is stronger than a 4 mark bolt, and it belongs where the factory used one.