They are size M18 with a metric fine thread pitch of 1.5. 

They are suited to Japanes bikes (rear shocks etc).  As they are stainless they will not rust.

Please consider using some anti seize compound, such as copper grease, on your fasteners.  It is well worth it to help ensure they do not seize up. 

They are nice quality. If you are not entirely happy with the pack you can return it for a full refund.