Dynamic Block Question

Does anyone know if you can add selection boxes or pick boxes to a block?

Here's the situation. I have a block that will be inserted showing a piece of angle iron that is used for a stiffener. We have various sizes that will need to be used. Instead of typing in the angle size each time it's inserted can I have a list of all the angle sizes and then a pick box or radial dial or something to be selected and that is what is put in the block?

Use Visibility and/or Lookup parameters.

I was wondering what Lookup Parameters were all about. I'm pretty new to the Dynamic Block making.

Thanks. I will check that out and see what I can do with it.