Step 3: Horizontal tube (bicycle rack)
Bike on stand is clamped by skewer to 100mm axle and also from the other side supported under bottom bracket.
I've measured all 4 bikes I have (frame sizes vary from small to medium: Mongoose M trekking, specialized S road, Giant M road, Giant S MTB ) and is more less similar distance ~60-65cm between bottom bracket and fork axle. Fortunately the weight stands had adjustable height so I've made the horizontal pipe adjustable for future flexibility.
details of the axle and skewer you can see on the picture and sketch.
Because the smaller pipe was slightly wobbly I attached pieces of plastic at the end.
On the other side I screwed two pieces of thick plastic to support under bottom bracket and make a gap to prevent cables touching the rack (see photo)