Sizing a hinge-sighting drill

[Pipe Wrench]

I don't know how hinge-sighting drills are sized. Are they sized by the drill bit diameter or by the sleeve/guide diameter?

I have a broken-off M10 automotive steel bolt that has broken off 1/4" down the threaded hole of the aluminum transmission case. When the bolt broke off it took with it 1/4" worth of threads from the hole. The diameter of the hole is 9.8mm.

1. What size hinge-sighting drill do I need to buy that will fit the 9.8mm hole?
2. Can I get a left-handed drill bit for any brand of hinge sighting drill sleeve? Any recommendations?
3. Is there a better type of self-centering drill or other option to get the hole started in the broken bolt? If I only use a punch I'm afraid the drill might slip.

Here is a picture of the broken-off M10 bolt:



Thank you!

 

[gizardlizard]

Don’t even need a hinge sighting drill. Here’s a trick we use at work all the time on broken off recessed bolts. Take a bolt of the same size, chuck up in lathe and using a center drill, drill it. Then follow it up with whatever size drill bit you want. That part depends on if you’re using an extractor or a left hand drill. The piece you just made will allow you to drill straight and in the center. Before you use it, just be sure the broken bolt doesn’t have a steep face to it. It needs to be remotely close to flat. This system works great.

 

[RTM]

Learned a New term today. I’ve always heard them called self centering bits. Mine are sized by the bit diameter, and one just by screw size. Not sure they would give you the satisfaction you need for drilling out a screw in those conditions.