I am not aware of an online source.  This forum is probably your free source.  The American Institute of Steel Construction (AISC) has published an historical record of dimensions and properties of rolled shapes.  The book is titled "Iron and Steel Beams 1873 to 1952".

The following editions of the AISC Steel Manual contain the 6B12.

2nd ed. 1934
4th ed. 1941
5th ed. 1947
6th ed. 1963

It probably is also in the 3rd edition, but I don't have a copy.

The properties are:

Depth 6.00 in
Width 4.00 in
Area  3.53 in^2
Flange thk 0.279 in
Web    thk 0.230 in
Weight 12 lbs/ft
Ixx 21.7 in^4
Sxx 7.24 in^3
rxx 2.48 in
Iyy 2.89 in^4
Syy 1.44 in^3
ryy 0.90 in

There is a Wide Flange beam (W6x12) with very close properties in

7th ed. 1970
8th ed. 1980
9th ed. 1989

Thru the 5th edition, Structural steel was A7 (yield 33ksi).  The 6th edition recognized the use of A36 (yield 36ksi).

A good source for out of print books is: www.mxbf.com

Thanks for the tip. I was hoping that old data might be available on-line somewhere. I guess I'll have to bite the bullet and order from AISC.
Thanks again.
David Anderson

You may want to check the used book dealers on the web for a copy of one of the older AISC Steel Construction Manuals.  I have three old ones I got at tag sales over the years and once in a while they come in handy.

Try the site listed below.

http://www.bibliofind.com/

It seems like you got the answer.  Why do you have to buy yhe book?