bolt and nut specifications

Only bolt diameter is not enough.

What is the strength requirement ( You have to go through the joint design).

Assuming you have it , then based on the strength you can go to any site and have the standard bolt head sizes.

I think you are asking for

Thick ness - bolt head ?

Width - Bolt Head (A/F - across flat ?)

Length of what ? Bolt ? will design for the application, more important is the thread engagement length

(for head sizes- UN)

http://www.derose.net/steve/resources/engtables/bolts.html

(For Strength etc - UN)

http://euler9.tripod.com/bolt-database/23.html

(Metric)

http://en.wikipedia.org/wiki/ISO_metric_screw_thread

http://www.roymech.co.uk/Useful_Tables/Screws/Hex_Screws.htm

(Head Dimensions)

etc/

PS: There is a previous link- still active on "Torque tensioning of bolts" check that up for further information

PS: Again- only bolt diameter knowing is not enough to design a bolt. It is rather the otherway round- you design the joint and then you land up in a number of various combinations-

eg M30- Gr 12.9 , or M33 Gr 10.9 , Or M39 Gr 8.8 , or M45 gr 5.6

or some times

M30-Gr 12.9- 12 Bolts, or M36 Gr 10.9 - 8 bolts etc.

Then you look for economics and decide (provided the joint strength is same for these combinations)

Note: Values are given as we call in engg NTS (Not to scale) so don't consider the values only the concept