Stuart France said:
Well, I thought 'aerospace' was clearer in this context than '6061-T6'. It all arrived adorned with bar coded sticky labels in 2ft lengths. Sorry to disappoint, but there were no mixs-ups in the warehouse.
Sorry Stuart - my comments on aerospace grade Al weren't meant to be a swipe at your choice of metal or identification, just a reflection of my dislike of "aerospace grade aluminium" by people selling a product, as it's inherently meaningless.
But as someone who has had trouble sourcing 7075 T6 in smaller quantities I sure understand the struggle in getting your mitts on certain materials.
Stuart France said:
Incidentally, I'm not aware of any commercial rack designs that use only a single metal.
The BMS rack I asked about in this thread and have now bought and used is all stainless steel. The manufacturer BMS does not disclose which type(s) of stainless, and if you wanted to be pedantic it could be pointed out that the components are probably made of different stainless steels.
BMS micro rack preliminary wear and handling
I've now used the BMS for 360m of descent (completely on rope). 180m on 9mm, 180m on 10.5mm. It handles both diameters really well, on the 10.5 you're starting to run out of space for locking off, but it's just about enough to pass a loop between the bars.
The wear on the bars is already visible, this is for pretty clean but not pristine ropes. Spent a thrilling half hour or so taking some measurements, mean wear is 0.135mm.* The wall thickness varies between 2.80 - 2.88mm. The bars can be flipped, but you also don't want to wear all the way through a bar on either side, so for argument's sake let's say the maximum wear before retirement is 2.80mm, meaning you'll get 7.5km of descent on clean-ish ropes. More if you predominantly cave in nice clean washed Yorkshire potholes using freshly washed ropes.
Althought I keep a log of all my caving, I didn't write down when exactly I replaced parts on the Petzl Stop. As an extremely rough ballpark under comparable conditions the top aluminium bobbin was good for maybe 1.5km, and the stainless steel handle one for 3-4km.
Info of use to absolutely no one:
The bars on the BMS can visually be identified as straight seam welded pipe. There is no benefit to using seamless here, so good price choice. Deviation from roundness 0.12mm +/- 0.02mm.
*mean wear over all bars compared to averaged measurements of ODs. Don't ask me about the uncertainty, there is enough overanalysis here already.