Late entry here, but...
Screw-in chokes in general are somewhat fragile and those thin wall abominations are particularly so. I've passed on more than a couple really excellent guns at really excellent prices simply because they had those things cut into them. And make a quick guess as to why the prices were so excellent.
Just sayin'
Fragile .......... maybe, if you're the kind of person that can tear up an anvil in a sandbed. I own somewhere around 30 choke tubes ......... CompNChokes, Kicks High Flyers, factory tubes, Briley S1 thin walls, etc., and numerous guns that use them. I've never damaged a choke tube, or even come close. When they're not in a barrel they are in a protective box. Fragile? I think not. Nice wine glasses are fragile. Thin wall chokes an abomination? Coming from one who thinks he can unlock the mysteries of the cosmos, that's really a hoot.
