I needed a third layer on my Ultimate Support Ax keyboard stand. I purchased the original stand back in 1991 and was pleased to see that I could still buy accessories for it including the add-on clamp and these tri bars.
Note : there is a small 'bump' in the bar that hooks into the clamp. I can only guess that the design changed slightly since 1991. I had to cut this out with a knife so that I could insert the bars into the clamp on my stand. Once removed they fit perfectly. Used them for a gig first time last night. No issues.