Markus, From what information I can gather Fox originally used the flat base kickstand along with the U-shaped channel to allow the leg to hang down below the bottom of the motor plate. When they started making models like the Trail Bug which had two downtubes from the steering head to the motor mount they used the W shaped base without the U-shaped piece...see pic below. Over the years I've seen Foxes with different combinations of the two types of bases and with and without the U-shaped channel. The problem with using the flat base with the U-shaped channel is that U tended to squish out along the sides as the bolt was tightened and the kickstands were always loose. I'm using the flat bases on my bikes but instead of the U shaped spacer I'm using a two inch long piece of 1-1/2" X 3/4" X .049" rectangular chromolly tubing. That way the bolt can be tightened sufficiently without the spacer squashing and loosening. I see you have a nice selection of kickstands there. Want to buy a cheap, slightly used, bender...lol. Ogy