I purchased these Field Notes Brand memo books and love them but I didn't like the way the books didn't stay closed and pens clipped onto the books awkwardly. So I quickly designed up this clip that not only keeps the book closed but also lets you attach a pen. I designed the clip to perfectly fit the Field Notes Brand click pens but as you can see it will also fit other brand pens too.

There is also a clip that eliminates the pen pocket incase you don't need it.

I included the parametric Pro/Engineer CAD files for those interested in modifying the design or adapting it to other memo books and pens.