Of all the unmitigated gall!

 I have, or had, a carbide insert cutoff tool for the lathe.  When I first installed an insert, I found it very difficult to tighten the T20 clamp screw.  This turned out to be because the web of material which acts as the hinge for the clamp finger was made far too tight; we are trying to bend a piece of hardened steel half an inch wide and about a tenth of an inch thick.

 The usual "flag" wrenches haven't got nearly enough torque/length to get the screw tight enough for the insert to not fall out.  And so, wrather than fix the assembly line and the part, they just put a long wrench in the kit.   It appears to be made of stainless steel.  How thoughtful.  The reason Torx™ and similar wrenches are made from tempered carbon steel is that, when one applies large forces to a stainless tool, this happens:

  Unfortunately for me, the screw itself is stainless steel.

WHY OH LORD?!?

 Stainless steel is a gummy metal.  It galls under high pressure, and the deformed / excavated material then jams between the fastener and the hole.

 That wrench deformed because I was putting a lot of torque on it (just with my hand!) but the clamp screw is utterly jammed and will not come out of that hole for love nor money.

 I tried several methods for breaking or cracking the insert in hopes that relieving the resisting force from the clamp finger would help to unjam the screw, but the insert seems remarkably tough now that I want it to break.  Where was this toughness when I was trying to use it?  Ahem.

 So this tool was turned to scrap the very first time I wanted to swap out the insert, because idiots in China couldn't do a very simple job right.  Grrr.  Of course, I could have bought a tool from Kennametal, Sandvik, Tormach, etc. and I wouldn't have this problem.  I would also have an empty bank account.

 Now in theory, I could drill out that stress relief hole and/or mill the back side toward the hole, to thin that "web" of material.  This requires a carbide drill or mill tho, as the tool is hardened.  AFAIK.  I'll give it the ol' file test when I go back out to the shop.  Unfortunately, only the milling option seems likely, I haven't a lot of carbide drills, and that interrupted-wall hole looks like a great way to break carbide bits.  And if it is hard, you just know The People's #1 October Brigade Drill Factory will not have tempered it one bit; it will be as hard as cancer.

 If I could get that @#$%!! screw out, I could replace it with the proper black oxide carbon steel screw.  But I don't think I can get the screw out, short of drilling it.  Since the tool is scrap anyway, I will definitely try that maybe even today if I can pull my thumb out.  I've made a concerted effort at removal already, so drilling seems like the next thing to try.

 But I admit my Torx™ tooling is limited, so I might go buy a set of folding Torx wrenches.  I tried a T20 bit in a 3in long Craftsman ratcheting offset screwdriver (as shown in photo), and the screwdriver soft-failed at a pretty high degree of torque. (junk, do not buy, I need to replace it when I win the lottery).  I did the usual things: applied penetrating oil and vibration, tried to work the fastener back and forth, tried heat too, all to no avail.

  Worse luck: stainless expands faster than carbon steel so heat is not going to help here; the screw will just swell in the hole and be even more jammed than when it is cold.  Just my luck.

You may or may not get what you pay for, but you certainly won't get what you didn't pay for.

PS: I should probably save up for a blade-type cutoff tool.  No clamp screw.