Bolts for joists?

[Hpd]

I’m building a flat roof which spans 4x4.5m

I have been told to use two 8x3 joists to trim out for a roof lantern going in the middle.

What size bolts should be used to bolt these timbers together? Also what spacing?

Thanks!

 

[bobasd]

you can use m12 - 250mm threaded rod packsfrom amazon.
use m12 timber connectors - square plate washers an nuts to suit.

drill at 30mm from top or bottom edges an space holes on 600mm centres