This model is to replace the cap on the Microsoft Slim Pen 2. I was asked to make a print to fix a pen cap that was shattered, and this is what I came up with. You may find that you need to force the cap on, but that is by design. This model also utilizes the little metal piece that was loose inside the original cap to click the button. 

I don't have a lot of experience making and posting 3D parts, so any constructive criticism on the part or post is welcome.