I’m in the middle of swapping a B20B into my 1993 civic, and I had to buy (just about) every bolt / nut on the engine and transmission since I was missing so many. I also had the pleasure of tracking down all this information from various forums and sources. To try and help any others who are partaking in a similar project I’ve compiled a list of what I found below.

These specs are for a B20B with a B18B1 (ls) intake so in theory it should cover most B-Series stuff. It also applies to some D-Series stuff (throttle body, etc).

Understanding Metric Bolt Sizes

Metric bolts are measured in “M” sizes.

Ex: m6x1.0x16

• m6 indicates that the bolt has metric threads, and has a shaft diameter of 6mm.
• 1.0 is the thread pitch.
• And lastly 16 is the length of the bolt (16mm). (The head is not included in the bolt length)

For more info please see: https://www.boltdepot.com/fastener-information/measuring/notation.aspx

Regular and JIS Bolts / Nuts

If you’ve ever had to replace a bolt or nut on your Honda with one from a hardware store you may have noticed that the head on the new hardware requires a larger socket than the original one from your car.

This is because Honda bolts are JIS spec, and most hardware stores don’t carry this. It’s perfectly fine to use either, but if you’d prefer to keep them all the same head size I’d recommend sticking with JIS but that may require ordering them online.

Intake Manifold Studs

If you have the OEM studs:

• (9) m8x1.25 flange nuts

Or if you deleted the studs:

• (9) m8x1.25x30 flange bolts

MAP Sensor

• (2) m4x0.70x12 bolts (15mm works too)

FITV

• (3) M6x1.0x38 bolts (40mm works too)

Throttle Body:

If you still have the OEM studs:

• (2) m8x1.25 flange nuts
• (2) m8x1.25x30 flange bolts

Or if you deleted the studs:

• (4) m8x1.25x30 flange nuts

IAT Sensor:

• (2) m6x1.0x16 bolts

Fuel Pressure Regulator

• (2) m6x1.0x16 bolts

Exhaust Header

If you have the OEM studs:

• (9) m8x1.25 flange nuts

If you removed the studs:

• (9) m8x1.25x30 flange bolts

Valve cover:

• (~8) m6x1.0 acorn nuts (amount varies by valve cover!)

Distributor:

• (3) M8x1.25x28 flange bolts (30mm works too)

I’d recommend flange bolts over hex heads unless you make sure to run washers with the hex heads.

(2 Bolt) Driver Side Engine Mount:

If you still have the OEM studs:

• (2) m12x1.25 flange nuts

If you deleted the studs:

• (2) m12x1.25x30 flange bolts

Bell Housing

• (5) m12x1.25x55 flange bolts

Starter

• (1) m10x1.25x110 flange bolts
• (1) m10x1.25x45 flange bolts

Transmission Rear Mount / Bracket

• (2) m14x1.25x67 flange bolts (70mm works too)
• (3) m10x1.25x35 flange bolts
• (1) m12x1.25x97 flange bolts (100mm works too)

Transmission Top Mount

If you’re running the OEM mount with the studs:

• (3) m12x1.25x20mm flange nuts

If you’re running a billet aluminum mount and removed the studs:

• (3) m12x1.25x35mm flange bolts**

**Billet aluminum mounts are thicker and require longer than stock bolts to compensate.

Clutch Slave Cylinder

• (2) m8x1.25x25 flange bolts

Speed Sensor

• (1) m6x1.0x30 flange bolt

Front Torque Mount

• (3) m12x1.25x20 flange bolts

Ground Strap

• (2) m6x1.0x16 flange bolts

Not listed above?

There’s too many bolts and nuts to cover them all, but given Honda doesn’t use many different sizes / thread pitches it’s not too hard to figure out what a bolt is.

The most common sizes and pitches are:

• m5x0.8 (Tiny bolts / screws typically found in small places like sensors)
• m6x1.0 (The 10mm bolts all over the car)
• m8x1.25 (Slightly larger common bolt size. Found on the bumper braces, battery tray, suspension, and more)
• m10x1.25 (Starter, suspension, etc…)
• m12x1.25 (Larger suspension bolts, bell housing, side engine mounts)
• m14x1.5 (Big bolts on rear engine mount, suspension, etc)