Which parts have no-friction Technic axle holes? I want to make a no (or very low) friction inline coupling for axles.  The axles must turn, transmit moderate torque, and be in phase (therefore backlash must be minimal).  The axles remain inline at all times.  The axles do not need to slide when in use; the no-friction requirement is just for easy (dis)assembly.

The coupling must be very compact, especially in width (not greater than 2 studs wide).  So I am interested in parts with no-friction axle holes.

I am aware of the following parts:


32905 Screw Gear.  This has the disadvantage of being > 1 stud wide,
so cannot have beams or connectors immediately adjacent.
32494 Steering CV Joint.  Together with 92906 CV Joint Axle the assembly is 1 stud wide, but needs "bracing" to keep it inline.


Are there other parts with no/low-friction axle holes that could be useful for this coupling design?  Or are there alternative coupling designs that meet the stated requirements?
One possibility is the Technic, Gear 8 Tooth without Friction. It was specificially designed to allow axles to slide through it. It can be held by 4 other 8-tooth gears, one of which could allow for the mechanical connection:

 o 
o+* 
 o

+ This is the frictionless 8-tooth gear your axle can be inserted into
* This gear is used to transmit the torque via another, fixed axle
o These are gears pinned to the frame but connected only to the central one


The above solution does violate the 2 studs width requirement, but it still might be possible to use the gear with the fixed axle inserted by half a stud and the removable axle occupying the remaining half stud. This would require a way to fix the gear in place, since both axles would have the same amount of clutch, and depending on your definition of "moderate torque", the interface along the half stud length of gear and axle might prove insufficient.