Interesting post over at Cold Thistle about reverse thread screws (Grivel). I know you're locked in with BD, but the post is interesting as is the Chicks With Picks interview with Bill Belcourt of BD.http://coldthistle.blogspot.com/2013/11/ice-screw-technology.html
is the CWP interview. Interesting to here Bill not supporting the use of screamers.
And this re: screw length:
Last question – about screws. Is a short screw as strong as a long screw given the same quality of ice?
Bill: Yes. IF the ice is good, we pull-tested a short screw at 7-8,000 pounds and the ice is plenty strong and its just the wall thickness of the screw and the strength of the hanger that determines failure. Its not the length of the screw that determines failure. If the ice is good, then all screws are equal. Just like with bolts – with granite you can put in a 3” bolt, in sandstone you put in a 4-5” bolt. So the better the quality of the stuff you are putting the pro into, the shorter it needs to be to be full strength.
The threads – what role do they play?
Bill: There are some debates between reversing the threads, how high the threads are, the pitch of the threads all determine somewhat the strength, but also the place-ability of the screw – how many rotations it takes to go in. So the faster you pitch it the less rotations it takes to go in but the more force it will take to turn the screw as its cutting into the ice at a faster rate. Conversely, if you make the threads really fine, the crank pressure would be really low but it would take a lot of revolutions to get the screw in. So you are trying to look for an optimum balance between how much force it takes to crank something in with your hands and how many rotations it takes to get it in so you can get it in and clip it the fastest. As far as reversing the screws, vs with the steep side outward, we’ve frozen a block of ice inside a large steel case, put it in a pull-testing machine – clamped onto the head of the screw with angle iron because the hanger wasn’t up to the amount of force we wanted to put on the screw – and drilled a hole through the angle iron, which allowed us to pull straight out on the threads. In good ice, we pulled the screw to 7 or 8,000 pounds before we started bending the angle iron. Then we just stopped the test. So in good ice, an ice screws resistance to a straight out pull is really high – certainly way stronger than the hanger. The hanger is probably good for 3 to 4,000 pounds. The screw was good for far more than that in a straight out pull.
The mountains - whose summits reach or exceed arbitrary thresholds for elevation and prominence - are calling and I must go.