This question has popped up lately as you see images of people stacking two plates because they don’t want a single point of failure. Rescue 3 Europe tested stacked plates in cooperation with DMM and found that the double thick plates actually caused carabiners to fail at lower forces.
There are no moving parts to a rigging plate. It’s a hunk of machined aircraft quality aluminum. The forces it takes to break a plate would never be generated in any sort of rescue or rigging situation. It’s a classic case of if one is good, two is better. Except two is not better, two is worse.
The plate in this test was sold by CMC Rescue in the mid 1990’s and has been used for training by Tom Pendley for close to 30 years. It’s a monolithic piece of aluminum that shows wear and has been well used. It has no ratings or markings other than CMC rescue on it because when it was made, that was not required. In the 1990’s (and still today) rigging plates are in the NFPA auxiliary equipment category and only need to meet 36kN mbs but they often far exceed that strength.
It’s good to see that a machined piece of aluminum worked hard over 30 years is still unquestionably sound as a master point.
What about old dog bones?