It’s a safety thing. You bolt the caliper to the frame with a specific Shimano bolt, then this goes in after, it stops the bolt falling out if it comes lose.
Cargopile1314 came up with the correct answer and included a diagram.
Cotter pin goes into a grooved area of the adapter mount bolt, to keep the bolt from coming out if it comes loose.
That is why my front flat mount caliper has a pin and my rear flat mount caliper does not have a pin. But…I can see you can also cotter pin the rear caliper using special caliper mount bolts with the groove at the tip.
4 Comments
It’s a safety thing. You bolt the caliper to the frame with a specific Shimano bolt, then this goes in after, it stops the bolt falling out if it comes lose.
This locking pin secures adapter screw in place
[Exploded view](https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://dassets.shimano.com/content/dam/global/cg1SHICCycling/final/ev/ev/EV-BR-R7070-4328E.pdf&ved=2ahUKEwiRibzewumKAxWwg4QIHdbFMsoQFnoECBkQAQ&usg=AOvVaw0Walm7S8oQbFGLkSRDZzM)
#19 engages with #20 after installation
Cargopile1314 came up with the correct answer and included a diagram.
Cotter pin goes into a grooved area of the adapter mount bolt, to keep the bolt from coming out if it comes loose.
That is why my front flat mount caliper has a pin and my rear flat mount caliper does not have a pin. But…I can see you can also cotter pin the rear caliper using special caliper mount bolts with the groove at the tip.
Thank You