Mdtryhht

I have noticed that there are a few LEGO pieces that also function in the "real-world." For example, the 10830c01 Magnifying Glass can actually magnify.

Another example is the 70001pb01 Compass, which works the same way you'd expect any "real-world" compass to function. (Although it's not always 100% accurate.)

Are there any other LEGO pieces that have "real-world" functionality?

One obvious answer is all components of the power functions family.

Lights can be used as lights, motors can be used as motors.

All Aboard!

I'd like to add my all-time favorite LEGO piece:

• x870cc02, THE BLACK WHISTLE!
  

The white brick is a microphone. Attach it to your train's motor and BLOW THAT WHISTLE! Depending on how short (or LONG!) your whistling was, the train would go forwards or backwards.

• Real-world use: Not only did it drive your train round the bend, but your parents too...!
  

I suppose several of the tools in Minifigure utensil wheel theoretically could be used in certain circumstances. I.e. you could hit things with the hammer, it would probably break before you got anything useful done with it, but it can still be said to have it's functionality.

Those shoehorn pieces worked. Technically, all of them serve their intended purpose as bricks. The ropes function. The ball shooting contraption present in the Lego Ninjago dragons (and other sets, I bet) functioned, as well as the spring-loaded cannon pieces. The axles technically worked (but not very well in actual cars).

The holes in Lego Technik work very well as holes.

By which I mean, I have built very successful motor-driven cross slides for small machine tools using Technik pieces.

When paired with nominally 4.8mm metric ground rod (which tends to have a negative tolerance) the 4.8mm holes are a nice sliding fit. Imperial 3/16" rod at about 4.76mm also works, but is a bit sloppier.

Although the hole is a little undersized for tapping M6 (5.0 required), the soft plastic easily allows a taper tap to be run through. The 1mm pitch of the thread, together with the hard metric 8mm width of the brick means that the start and finish phase of the threads is identical. If an already tapped bricked is pegged as a guide to a new brick, then (a) the guide will help ensure that thread goes in straight and (b) has the same phase in both bricks. I mark a guide brick, so there's no cummulative error in creating new tapped bricks.

A piece of 6mm studding can then be used as a lead screw. It can be fitted concentrically to Technik shafts by locknutting it to a tapped brick, then pegging the brick to a 40t gear.