Dad broke a hex key and further mangled a hex socket head bolt. I tried the hammered in torx bit, but that didn’t work. The screw is in a recess and can’t use pliers or anything to grip on the outside. So a screw extractor is needed IMO. But which type is better?

Straight fluted

or

Spiral fluted

Never seent eh top ones before, looks like they will do much the same as the lower ones.
The ones I used most were like this:

Joe, usually the best solution I’ve found is to hammer the hex key back in and then weld it to the head of bolt, it will usually come undone.

Straight flutes are for soft materials

Spirals are for hard metals

I prefer http://www.irwin.com/tools/screw-bolt-extractors/hex-head-multi-spline-screw-extractors-532-series-plastic-case-sets for my spirals – they just work.(pst hanson – invented the screw extractor in the 1940s. – and snap on even rebadge this set;))

Left hand drill bits are the way forward for drilling the hole – often this removes the offending item. If not you have a nice hole for the extractor to work in.

Top tip, buy good quality ones , dont force em, having had to pay to get a colleagues hamfistedness spark eroded out (a drill bit wont touch the hardened steel (cheaply hardened on cheap tools hence they go brittle and snap easier)

Spiral is the type I’ve got and used successfully. There didn’t seem to be any other option in the shop when I looked.

I had to drill pilot holes though for these to bite. Had to use Cobalt bit as the bolt was stainless steel and HSS bit I had was going nowhere. HSS can be used for softer bolts apparently. Small hole, give it a try, then bit bigger, try again etc.

It might just rattle out with drilling anyway.

Thanks, everyone. I think I’m going to get this set. It looks like the drill bits are regular right hand spiral, though…

After getting through a few admittedly cheaper long spiral ones I got some of the stubby ones linked to above by trail rat and they have been so much better.

The drill bits will be a normal twist , just drill a hole of the right size gently tap the extractor in square and then turn the extractor left. Slow and steady