what breaker for shower ?

I am having a shower fitted by a friend who is a plumber but he cant do the electrics so i am after some info towards this side of shower installation. I am using 10mm twin and earth coming out of a crabtree starbreaker fuse box, i have everything ready to install except the correct breaker. Can anybody tell me the exact specifications needed for this please, i know it has to be a crabtree starbreaker and i know it has to be at least 40a rated but does anybody know if it is type b or type c and what is the difference between 6ka and 10ka, thanks for any help

jules