I am building up a fatbike frame that has a twin top tube setup;



I am wanting advice on the material for the plate at the seat tube to top tube junction. The tubes are 4130 and Columbus Thron, and the plate will be fillet brazed in.

I have some AISI type O1 tool steel, but i am extremely reluctant to try and braze this and expect no cracking..

What should i be searching for?

http://pogwardbicycleindustries.blogspot.co.nz/