I like to use safety wire on critical fasteners used in assemblies like suspension. I am adverse to drilling 1/16" holes 1-1/8" deep through the heads of grade 8 bolts. I prefer to drill through the corner of the hex. This same methodology can be used for nuts. I purchased a drill jig for this purpose but was not satisfied with the results. I broke too many drill bits ruining expensive bolts. I came up with a successful methodology using my milling machine. I find the edge of the hex point and move into the bolt 1/8". I mill a flat using a solid carbide two flute Kennametal end mill which makes a flat. I then step back another .020" and drill a 1/16" hole using a Guhring parabolic flute drill bit. I have drilled over two dozen holes without breaking a bit. I keep the speed down to 1,500 rpm and use synthetic gear oil to lubricate both the end mill and drill bit.
The aluminum jigs sold for this purpose are JUNK, do not waste your money on them. I have and use a WWII era surplus jig, made of tool steel, for this purpose.
The aluminum jigs allow the drill to "wander", enlarging the jig hole in the fixture. Drill breakage starts immediately thereafter. Also, "low twist" (helix) cobalt drills with 135 degree point angle work best for me. I could probably make a 118 degree, regular twist drill bit work in a pinch, but DO NOT use high helix drills, as they are very "flexible". High drill bit rpm, light feed rate and cutting fluid definitely help drill bit life and reduce drill bit breakage. Instead of the end mill trick to start, a small diameter center drill can be used. Again cobalt, high rpm, low feed and cutting fluid are required.
If you are drilling a
LOT of Gr8 or hardened "Allen head" bolts, find or machine a tool steel fixture, and get the cobalt drills. You will save your sanity in the long run.
Just my 2¢
Fordboy