The original caps look like this. There is a fin on it that prevents the pen from rolling away – only when it’s screwed on the business end.

As you can see this is not actually a pocket clip, and also the cap cannot be “posted,” that is, stuck to the tail end of the pen body. You can balance it there, but it doesn’t lock or or grip so it won’t stay there and just falls off. So you can’t carry the pen in your pocket without it becoming annoying (although it is quite long, sized and shaped more like a dip pen nib holder, so make sure you have deep pockets) and you can’t mount the stock cap on the tail to keep the pen from rolling away if you’re using it on a sloped surface like e.g. a drawing or drafting table.