/ Express ice screws
By the discernable difference in the effort required to place the screw. If you hit an air pocket you can tell, it starts turning much easier.
you can always tell if you hit a large air pocket, ice stops coming out of the head and the screw stops having any resistance to going in.
In fact this difference is probably far more noticeable with winding screws than those not, due to the smooth nature of placement, i.e. you feel the difference more than those which require endless hand cranking, because feedback from the screw is more constant.
It is really obvious when you screw into something really duff.
It's a problem that's easily fixed.
Just take a file to the teeth and blunt them off a bit. I'm sure you'll appreciate the extra feedback your get when you place them.
Having borrowed someone's spare screw (that is to say the blunt one) last winter, I can't say that it was an improvement in any way.
I know I was just showing off my "old timer" credentials. :-)
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