Here is the list I feel should be snap-on if you can afford it. Just about everything else, you are paying for a name and for the easy credit. In these kind of items that are pushed to their breaking limit regularly that 2% BETTER QUALITY that snap-on may offer on these items will make life easier for him once or twice a year. That adds up to quite a few hours saved over a career, where a lesser quaity tool may have failed or stripped the fastener.
Also remember, nearly everything made by snap-on can be purchased new or near new on ebay for less than the student discount...so do not think you have to use it.
I would by very little snap-on, it is overpriced because of the easy credit gimick and deliver to your door service. The tools, while very high quality, are often twice the price (or more) of other pro tools that are just as good. Things like ratchets, many less expensive ones available that are as nice or nicer and do the job just the same. Just buy Snap-On where they offer a good value.....things he will use hard EVERY DAY or things that are used a fair amount that get pushed to the breaking point. I would think with the student discount, for between $700 and $1,500 you should be able to get him about everything that snap-on sells that a new mechanic should have in snap-on tools. I would say get more, because at 50% off they are no longer stupidly overpriced, but the simple fact that all can be purchased on ebay for that any day, no need to rush....
Hex keys and sockets (gold colored ones)
Torx sockets (gold colored ones)
Screwdrivers (There are others as good, but they are a wear item and easy to replace)
Any wrench with open ends or crowsfeet
Line/flare nut wrenches and sockets
Picks
Tripple square sockets
Taps, dies drill bits and thread chasers (not because they are better, but because they break and wear out and Snap-on is about the only company that will replace them without issue.)
Many times mid priced items like Channellock and Craftsman items will be just as good and most of the time Matco, Proto, Wright, Cornwell will be just as high quality.
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