MANY months ago I bought a Gartrac seat mounting kit. I cannot find the 8 square mounting plates that fit on the ends of the bars. Dont know whether I have misplaced them or if they never arrived (had a couple of other issues with that particular order

I will make up some plates. Anybody know what size I should make them?? The regs do not appear to give any specific requirements other than the competitor ensuring it is safe. I was thinking something like 50x50x3????