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Discussion Starter · #1 ·
Hello all,

I'm building a gravel bike and encounter two issues for mounting disc brake.

1- Fork will only accept an M4 bolt in the brake caliper mounting inserts.

2- Flatmount type rear brackets wholes wont let an M5 (only M4) bolt through and the adaptor that came with the caliper will fit an M4 bolt only!

The brakes are TRP Spyres. On top of that the bolts that came with the brakes are M5, so nothing fits. My first experience with disk brakes, not off to a good start so far.

Who in the world uses M4 bolt to secure a disc brake caliper to the frame? I thought they were used for fenders and bottle cages.

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