Me please 
(I’m in Vietnam but gifting to my friend in the US)
I’d have to do some research to find the article again but the “hook tool” is also referred to as a “package carrier”. A search using that name might be of help. I want to say that the hook disappeared for a while and came back in the early 90’s. I think that makes your knife about 30 years old. I’m no expert but maybe this will help you do a search that gives you a real answer.
SMM
The Climber has arrived safe and sound. Thank you!