Difference between Allen and Hexagonal Bolts

Application (top/side clearance) and user preference.

I hate hex head bolts almost as much as I hate flat head screws!

I've also found that cheap Allen Head bolts (socket head cap screws) are usually tougher than cheap hex head bolts.

Talk to a fastener supply Rep. for bulk prices and general info.

Look in a copy of the Machinery's Handbook for detailed info.

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Kind Regards....

Hmmm, yes, the question is too easy to be from someone who's not a student. However, just to comment on details about the things that I didn't get from school and only learned from the school of hard knocks:

• Hex head bolts have generally bigger heads than allen heads. Makes it unsuitable or difficult to use for small equipment.
• I can use a number of different tools to move a hex head bolt but am limited to only two for the allen head (an allen key or a small (very small) pipe wrench).
• Most allen head bolts are recessed or "buried" while hex heads are usually raised. If a hex head is worn (rounded), I can use other tools to get it off. However, a recessed and worn allen head is a very big pain to remove. There's a special tool for this but I usually can't find it (someone else is using it).
• In tight spaces, hex heads are difficult to remove since a wrench needs space around it to turn. Only option in this case is to use a socket wrench with an extension. Allen heads don't need much space for the allen wrench.
  

Torx (star) bits can be used where the damage to an allen head is not too severe. The slightly tapered design allows for "remodelling" with gentle application of a "Glesga screwdriver" (hammer).

ROFLMAO @ 'Glesga screwdriver'

First time I've heard a hammer called that !!!