Stratocaster Bridge plate string breakage

Branshen

My mim standard stratocaster just broke a fairly new b string at the bridge plate. 

What's the best way cure string breakages that's caused from the string rubbing on the bridge plate?

I can see a little notch in the metal of my bridge plate where the string comes out from the trem block.

Do I file it flat? Change the plate? Put some sort of rubber over the string which goes over the plate? 

ICBM

Take the saddle off and use the tip of a round needle file to carefully smooth out the edge.

It might be worth doing the E and possibly the G as well - the wound strings are usually OK but if you're really thorough you can do those too.

Branshen

Thanks @ICBM. I'll invest in a file. Seems simple enough..