A bike has dozens of screws, and every one of them matters
A bicycle may have more screws than you’d expect. From the stem to the bottle cage, from the brakes to the derailleur, every screw has its own size and torque requirement.
Common Screw Sizes
| Size | Head Type | Common Location |
|---|---|---|
| M4 x 0.7 | 3mm hex | Derailleur limit screws |
| M5 x 0.8 | 4mm hex | Stem, seatpost clamp, bottle cage |
| M6 x 1.0 | 5mm hex | Disc brake caliper, rack mounts |
| M8 x 1.25 | 6mm hex | Crank fixing bolt (on some models) |
| T25 Torx | Star-shaped | Disc brake rotor bolts |
Screw Materials
| Material | Weight | Strength | Price | Best For |
|---|---|---|---|---|
| Steel | Heavy | Highest | Low | High-load locations |
| Stainless steel | Medium | High | Medium | Corrosion resistance |
| Aluminum alloy | Light | Medium | Medium | Non-critical locations |
| Titanium alloy | Light | Very high | High | Weight savings |
Note: Aluminum alloy screws are not suitable for high-load locations (such as stem fixing bolts). The few grams you save aren’t worth the safety risk.
Torque Quick Reference
| Location | Torque (Nm) |
|---|---|
| Stem fixing bolts | 5-7 |
| Stem top cap | Finger-tight only |
| Seatpost clamp | 3-5 (carbon) / 5-7 (aluminum) |
| Bottle cage | 3-4 |
| Disc brake caliper | 6-8 |
| Rotor bolts | 2-4 |
| Crank bolts | 12-14 (Shimano HT2) |
| Pedals | 35-40 |
Screw Maintenance
| Item | Method |
|---|---|
| Anti-seize | Apply grease or anti-seize compound to metal threads |
| Carbon fiber parts | Apply carbon assembly paste to threads |
| Regular checks | Verify torque on critical screws monthly |
| Rust prevention | Stainless steel screws recommended for Taiwan’s climate |
| Thread locker | Use Loctite Blue on locations prone to vibration loosening |
Frequently Asked Questions
Q: What do I do if a screw’s head is stripped (rounded off)?
- Mild cases: try a hex wrench one size larger
- Severe cases: use a screw extractor
- Completely unable to turn: take it to a bike shop
Q: A screw is rusted solid and won’t turn?
- Spray penetrating lubricant (such as WD-40) and wait 10 minutes
- If it still won’t turn, heat the screw head (use a hair dryer, not a torch!)
- Last resort: drill out the screw
A single small screw might cost less than NT$10, but the consequences of it being improperly tightened could be a crash.
Respect every single screw.
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