Explaining Frictional Torque at the Axle

[Amar.alchemy]

Let us consider a wheel which rotates about an axle thorugh its center with an angular velociy $$\omega$$₀. After sometime it comes to rest due to the frictional torque at its axle.
Now, if we go by the defination of torque than it is defined as:
$$\tau$$= r x F. Since the frictional torque is exerted along the axle, we can take the value of r as 0. Then there will not be any frictional torque. Kindly explain me??

 

[Doc Al]

Since the frictional torque is exerted along the axle, we can take the value of r as 0.

No you can't. Real axles with friction have non-zero radii.

 

[Amar.alchemy]

ok so, Frictional Torque is equal to the cross product of radius of axle and frictional force... Thanks :-)