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 and Exhaust
Manifold 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
Engine
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) Engine Mount:
If you still have the OEM studs:
- (2) m12x1.25 flange nuts
If you deleted the studs:
- (2) m12x1.25x30 flange bolts
Transmission
Bell Housing
- (5) m12x1.25x55 flange bolts
Starter
- (1) m10x1.25x110 flange bolts
- (1) m10x1.25x45 flange bolts
Rear Mount / Bracket
- (2) m14x1.25x67 flange bolts (70mm works too)
- (3) m10x1.25x35 flange bolts
- (1) m12x1.25x97 flange bolts (100mm works too)
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
The billet aluminum mounts are thicker and require longer 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)