Fitting a new mainspring

[TheFixer]

What's the best way to go about fitting a new auto mainspring? that's retained in a ring.

Stock photo.

[Nucejoe]

Get all the barrel greasing done, place the ring on barrel, rightly position the spring coil to enter the barrel ( nearly 0.75 mm of the coil enters the barrel) push the spring home, preferably sandwich the barrel and coil between two prongs of your tweezers to push on top of the spring. Next you insert the arbor in center of the coil.