by snoboy » Sep 11, 2012 7:28 pm
Mike:
Your query is very relevant to what I am doing at work this week. We are removing an old sprinkler system from the ceiling of an industrial building. As we cut each piece away we have to lower it to the ground. We are attaching to it with 8mm - 6 wrap prusiks on 6 & 8" pipe, then lowering them. The pipe is hanging vertically from one end, and we are getting no slippage.
So... I would say there is one data point for you - 8mm works well on 6-8"pipe. I would probably stick to that or 7mm, just for the anchor strength. a loop of that is equally matched in strength to a knotted 11mm rope (+ or - of course).
Another product on my radar, but with no personal experience of it yet, that I suspect might work well for what you want to do is Sterling's Hollow Block. Possible cons are limited length, and being aramid (kevlar) it may not be super durable.
If you want to load something along it's long axis I would avoid the Clove Hitch, and look at something like a Rolling Hitch.
I'm sure you are on this, but don't forget to verify the structural integrity of the metal you are considering for an anchor! Also relevant to this week's work! ;)