What is the density of high tensile steel grade 8.8?

Grade 12.9 fasteners can be any alloy steel, quenched and tempered. The density of 4130 (a relatively common alloy steel) is 7.85 g/cc.

Here's a data sheet for 4130, in case you were curious:

http://www.matweb.com/search/DataSheet.aspx?MatGUID=284aa856470341acbf3c16bc90849ea1