Corporate Gift Giving as a Junior

I tend to be very generous by nature when it comes to giving gifts which is not always appropriate in professional settings I had a former colleague help me out with something quite major (law related)- he probably incurred some costs and of course his time and effort. He did not have to do it, though it is not completely non-altruistic on his part. We are not friends we were involved in the same project at the law firm I used to work at. I wanted to buy him a small gift eg a pen or bottle of something as thanks - is this appropriate?