6-lug wheels are measured like 4-lug wheels. Bolt pattern or bolt circle is the diameter of an imaginary circle formed by the centers of the wheel lugs.. Note: When measuring a 5-lug wheel the measurement is only an estimate unless accurately measured using a bolt pattern gauge. A bolt pattern gauge is a specialty tool and is not widely available.
Palpation should be done using the fingertips and intensity of the pulse graded on a scale of 0 to 4 +:0 indicating no palpable pulse; 1 + indicating a faint, but detectable pulse; 2 + suggesting a slightly more diminished pulse than normal; 3 + is a normal pulse; and 4 + indicating a bounding pulse.
The grade is basically a measure of the strength of the steel used to make the bolt. There are specific industry standards for each grade, and even standards above and beyond grade 8. The fasteners you will pick up at the local hardware store will probably be grades 2, 5 or 8.