A handy tool that sits on my desk at work and has been used daily by customers and me for the past 3 years. Has all standard imperial sized bolts you'll ever find (or be able to carry), and a really easy way to determine the thickness differences between different gauge steel. This has both been a necessity at work and a learning tool for customers - and you don't have to move it from the desk to utilize all it's functions.

Their might be similar reference tools out there - but this one tackles all and any daily issue I may have conveying to the customer the answer they're looking for without having to say a word - (which comes in handy because I get people from around the world that speak different languages)