The weight rating of a single Oz Clip?

[Meg]

I had a client ask this recently; does anyone know the weight rating of a single Oz Clip (the large, 3 oz, 4" style)?

[T. Ashley McGrew]

I can provide this information for you. The problem is applying information to their actual use. Basically, as you could surmise, two Oz clips would be similar to the capacity of a two hole D-ring (actually more like a three hole, since being rigid, stresses is applied evenly to each screw) in application of course the weight of the painting is being supported by at least four Oz clips in standard use. In a static setting the amount of actual force required for an Oz clip to fail is very impressive. The part that is hard to calculate is the amount of force occurring in a dynamic setting. In other words the force of an object sitting still is a small fraction of the same object falling and coming to an abrupt halt resulting from a drop. Other issues that are critical are the stability of the wood that the clips are screwed to and the methodology involved (pre-drilled or not). Finally, in my experience, the most important measure of effectiveness has to do with the shock event itself. Almost every failure I have ever seen or heard about relative to Oz clip use was the result of a topple event where the crate fell over onto its face. As a result, the issue is not just the overall weight of a painting and a related calculation of the number of clips to use (four is the minimum not the optimal) but also the location of the clips. In many, many applications I have come across the use of four clips two on each side can be effectively supplemented by the addition of a single clip on the top edge of the travel frame. This is the area where the majority of force is applied perpendicular the the clips themselves in a topple event. Anyway if I haven't made it clear that there isn't a realistic simple answer (other than - don't just use four, use more on top, and pre-drill holes) then I will try and actually dig up some actual laboratory test results for what they are worth (purely static, vertical measurements). I will need to get permission to publish the results though since it is proprietary info as far as I know.

[GrahamBFAS]

In the example you quoted, did the Oz Clips fail or did the screws pull out from the frame?