DML FAQ : Chassis : One of my front lower shock bolts broke. How do I get it out?
If an E-Z Out doesn't work, you'll need at least a 3/8" (.375") dia. drill for the minor thread diameter. Actually, the drill/ream size is .377" + .003". If you do ream, leave at least .015" (.0075" per side) after drilling. Anything more than that & you'll trash your reamer. I'd suggest step drilling (1/4, 5/16, 3/8) to get everything out but the threads.
Sometimes a left-handed drill bit (if you can find one!) will "bite" & back a broken bolt out. Soak everything with WD-40 or some other penetrating oil first. Keep the WD-40 on hand and spray while you drill to dissipate the heat & save your drill bits (and reamer).
The actual thread designation is an M12 X 1.75. So you'll need a tap to clean the threads after you're done with the drilling/reaming.
If you bugger the threads, you'll need an M12 X 1.75 helicoil kit with a drill, screw thread inserts, an insertion tool & a tang break-off tool. Probably $50.
It's not easy to get at the boss that has the threads in it. I used a flat bar to push up & support the shock for clearance.
I don't think I'd try to heat the boss with a torch - too much rubber around - PLUS brake fluid in the nearby brakeline is highly flammable.
When I installed the helicoil insert, I secured everything with Thread-Loc 245 from Auto-Zone.