Machined bicycle disc-brake mounting boss and frame-side hardware

Disc Brake Mounting Hardware for Bicycle Frames

Post mount brake bosses, caliper adapters, and disc brake interface hardware for frame and fork OEM programs

## The Challenge: Brake Mount Precision at the Frame Level The disc brake mount may look like a simple threaded boss, but its dimensional requirements are unforgiving. Mounting face flatness, thread axis alignment, shoulder height, and boss-to-boss parallelism all directly affect brake performance. A 0.1 mm deviation in boss height shifts the caliper position enough to cause uneven pad wear and rotor rub. For OEM frame manufacturers, the brake mount is a permanent interface. Once welded, brazed, or bonded into the frame, replacement requires destructive rework. The mount must be right the first time.
## Key Disc Brake Hardware Categories ### Post Mount Brake Bosses Threaded bosses that provide the interface between the bicycle frame/fork and the disc brake caliper. Post mount bosses control caliper alignment, thread engagement depth, and brake torque reaction load transfer. - **PS-B Series**: 18 mapped brake mount SKUs with product renders and dimension drawings - Configuration: Post mount (74 mm bolt spacing) and flat mount interfaces - Material: Heat-treated alloy steel (42CrMo), 304/316 stainless, 6061-T6 aluminum - Process: CNC machined and heat treated; thread rolling or thread cutting per specification - Finish: Black oxide, ED coating (240h NSS), zinc-nickel plating ### Caliper Adapter Hardware Adapter brackets that convert between post mount and flat mount standards, or adjust rotor size compatibility. - **PS-B12–PS-B20**: Caliper adapters and conversion brackets for multiple frame/fork configurations - Thread types: M6 × 1.0, M5 × 0.8 per Shimano/SRAM standard ### Brake Mount Fasteners Mounting bolts and screws for caliper-to-adapter and adapter-to-frame interfaces. - **PS-A Series**: Button head and socket head cap screws in M5/M6 - Material: A2/A4 stainless steel or 10.9/12.9 grade alloy steel per specification
## Engineering Requirements for Brake Mounts | Parameter | Requirement | |---|---| | Boss height tolerance | ±0.05 mm (drawing-level control) | | Mounting face flatness | ≤0.03 mm across mounting surface | | Thread axis perpendicularity | ≤0.05 mm deviation from mounting face | | Thread engagement | ≥1.5× thread diameter into boss | | Torque capacity | 6–10 Nm per bolt (caliper specification dependent) | | Salt spray | 240h NSS minimum for coated parts (project spec) | **Engineering Note**: Final production dimensions, tolerances, material grades, coating specifications, and inspection criteria must follow the customer drawing and brake caliper manufacturer specification. The values above are series-level engineering references.
## ISO vs Post Mount vs Flat Mount | Standard | Bolt Spacing | Common Application | SKU Reference | |---|---|---|---| | Post Mount | 74 mm | MTB forks and frames (pre-2020 dominant) | PS-B01, PS-B02 | | Flat Mount | 70 mm (front) / 34 mm (rear) | Road, gravel, modern MTB | PS-B adapter bracket variants | | ISO | 51 mm | Older DH and early disc brake frames | Drawing-controlled custom | PremFixer can produce any interface geometry per the customer frame drawing. The PS-B series provides reference geometries for common post mount and adaptor configurations.
## Also Known As - Disc brake boss / brake mount axle / post mount boss - Brake caliper adapter / PM-to-FM adapter - Brake mount insert / threaded brake boss - Disk brake mount / disc brake adaptor (UK spelling)
## RFQ Checklist for Disc Brake Hardware - 2D drawing with boss geometry, thread specification, and tolerance stack - Brake mount standard (Post Mount, Flat Mount, ISO, or custom) - Caliper model and rotor size (140/160/180/203 mm) - Material grade and heat treatment specification - Coating type and salt spray hour requirement - Target annual volume and sampling quantity Submit Brake Hardware RFQ
## Related Series - [PS-B Disc Brake System Accessories](/products/ps-b-disc-brake-system-accessories) - [PS-A Standard Fasteners (Screws & Bolts)](/products#prod-grid) - [PS-H Spacers & Washers](/products/ps-h-spacers-washers) - [MTB Frame Fasteners & Suspension Hardware](/applications/mtb-frame-fasteners)