It should be a 6 mm bolt, but I don't know the length, and I don't remember if it is coated or made of a different material, as is common with battery bolts. I am a little worried about why you need it to be longer. Adding more than one or two extra terminals (eyelets) to a battery connection is an invitation for problems. The dissimilar metals in contact with each other corrode rapidly, due to electrolysis, and the layers attract moisture which also results in corrosion. Longer bolts and connections can also cause pysical damage to the soft lead terminals, due to added leverage and weight. It is better to install an auxiliary fuse block...and wire your additional loads to that.