Usage should be obivous.
Print with the flat side in the holes up and the spike oin the holes down.
Version 2 is less demanding to print in terms of sub-millimeter accuracy.
Because of the tall and slender nature of this thing you are advised to print with a raft even on a heated build platform.
Version 2.1 has an 0.5mm tighter grip on the rail.
It is also 7 instead of 5mm strong and increased the distance of ther hole-centers to the edge from 9 to 10mm to make it survive harsh battles.
No other changes.
Version 2.2 is even more sturdy at the expense of only 3 darts.
Feel free to change the design to any other length.
Exports to all major CAD format below.
Technical drawings with all dimensions and 3D PDF also below.