Hi
I am almost sure that Workhardt cartridges will fit in a Lilly pen (Humapen) as they are the same shape I believe as Aventis. There are a few posts on the forum with instructions for putting an Aventis (Lantus, Apidra) cartridge in a Lilly pen. All you have to do is attach a pen needle before you screw the pen together as a stream of insulin will come out the needle as you do so but once you have primed the pen you will be able to use it with no bother.