I have been looking to buy a new extruder. One of the options I have seen comes in "right handed" and "left handed". What does this mean? How can I tell what my current extruder is, so I get the right replacement?
This is an example of a right handed extruder setup:
And this is an example of a left handed extruder setup:
I believe that you can can choose whatever one you favor. With the right handed setup, you will be pushing down the red part with your right hand when inserting filament. With the left handed setup, you will be doing the same thing but then with your left hand. Personally, I favor the right handed setup (my right hand is my dominant and stronger hand). But, you should be able to choose whatever one you like! Be sure to check it will work with your printer though (extruder holder & hotend).
The short answer to identify what extruder type you have is the rotation of the extruder gear.
CCW rotation to extrude = right-handed extruder
Detailed explanation is below.
In addition to the other answers, the right-handed designation comes from math and pysics convention that has become a well known mnemonic in engineering practice:
or in its physics coat,
The Right Hand Rule: Figure (a) shows a disk is rotating counterclockwise when viewed from above. Figure (b) shows the right-hand rule. The direction of angular velocity ω size and angular momentum L are defined to be the direction in which the thumb of your right hand points when you curl your fingers in the direction of the disk’s rotation as shown. reference
In a right-handed extruder,
you place your thumb of your right hand in the direction of the shaft (so pointing it towards yourself in the image of the extruder above) to see that rotation in the direction of your curved fingers leads to extrusion of filament (in counterclockwise direction).
For a mirrored extruder they call it left-handed extruder.
It usually doesn't matter whether you get a right-handed or left-handed one. The reason the two different variations exist is because some people use a dual extruder setup. If you have two extruders it is convenient to have them be mirror images of each other (as this makes them easier to install in use with the filament release lever pointing out to the side). If you have only a single extruder, it doesn't really matter, unless there are other construction restraints.
when thinking about righ-handed extruder or left-handed extruder it's good to know that there is no magic or any other science rule behind this naming convention. it's just an arbitrary explanation which can be unfortunately misleading. in fact there is visual explanation of this left / right handed name and it doesn't have anything to any "the right handed rule" mentioned in other answers.
it's just this
no physics... no magnetism... no induction... no vectors and no formulas
the other answers present pictures of LH and RH extruders which are of course fine but be careful - there are universal extruders which can be both L or R handed.
like this one
as this extruder has fully fixed filament path and there is no restriction which direction the filament should go - there is no way to describe it arbitrarily
it is left-handed when it works as left-handed and it is RH when it works as RH